Uses the same technique used during OpenGL composition to elide root surface access. The refactoring of this approach is tracked in https://github.com/flutter/flutter/issues/38466

Fixes https://github.com/flutter/flutter/issues/39009.

We will end up creating fewer threads in tests.

No functional change. Just makes testing with fixture images easier. Adding a
whole lot more tests that use this path for the embedder surface rotation
patches. Want to land stuff in smaller chunks.

change_install_name.py was operating on framework library files
in-place, which breaks GN's timestamp analysis handling since a file
can't be both an input and output of an action. As a result no-op builds
on macOS were not actually no-ops.

This changes the script to operate on an output copy, both fixing the
no-op build issue, and simplifying the GN framework construction scripts
by combining the copy step and the install-name step.

Fixes https://github.com/flutter/flutter/issues/33465

Fixes https://github.com/flutter/flutter/issues/38870

The root canvas is managed by the external view embedder when using a custom
compositor. Due to this, frame submission on the surface will not end up
flushing the same (because the surface doesn’t have it to begin with). Fixed
with tests.

This test queues tasks to a custom task runner that runs the tasks on the
platform thread.  After shutting down the engine, the test must wait until
these tasks are drained before the test exits.

This issue would only manifest when a custom task runner was being used with
a custom compositor. Both were tested separately but not together. A new
test has been added for this. We still create the GPU thread merger
unnecessarily but I can patch that later. I also cleaned up the existing
custom task runner test to not submit tasks on a dead engine as they just
log errors unnecessarily.

Filed new: https://github.com/flutter/flutter/issues/38844

This patch allows embedders to split the Flutter layer tree into multiple
chunks. These chunks are meant to be composed one on top of another. This gives
embedders a chance to interleave their own contents between these chunks.

The Flutter embedder API already provides hooks for the specification of
textures for the Flutter engine to compose within its own hierarchy (for camera
feeds, video, etc..). However, not all embedders can render the contents of such
sources into textures the Flutter engine can accept. Moreover, this composition
model may have overheads that are non-trivial for certain use cases. In such
cases, the embedder may choose to specify multiple render target for Flutter to
render into instead of just one.

The use of this API allows embedders to perform composition very similar to the
iOS embedder. This composition model is used on that platform for the embedding
of UIKit view such and web view and map views within the Flutter hierarchy.
However, do note that iOS also has threading configurations that are currently
not available to custom embedders.

The embedder API updates in this patch are ABI stable and existing embedders
will continue to work are normal. For embedders that want to enable this
composition mode, the API is designed to make it easy to opt into the same in an
incremental manner.

Rendering of contents into the “root” rendering surface remains unchanged.
However, now the application can push “platform views” via a scene builder.
These platform views need to handled by a FlutterCompositor specified in a new
field at the end of the FlutterProjectArgs struct.

When a new platform view in introduced within the layer tree, the compositor
will ask the embedder to create a new render target for that platform view.
Render targets can currently be OpenGL framebuffers, OpenGL textures or software
buffers. The type of the render target returned by the embedder must be
compatible with the root render surface. That is, if the root render surface is
an OpenGL framebuffer, the render target for each platform view must either be a
texture or a framebuffer in the same OpenGL context. New render target types as
well as root renderers for newer APIs like Metal & Vulkan can and will be added
in the future. The addition of these APIs will be done in an ABI & API stable
manner.

As Flutter renders frames, it gives the embedder a callback with information
about the position of the various platform views in the effective hierarchy.
The embedder is then meant to put the contents of the render targets that it
setup and had previously given to the engine onto the screen (of course
interleaving the contents of the platform views).

Unit-tests have been added that test not only the structure and properties of
layer hierarchy given to the compositor, but also the contents of the texels
rendered by a test compositor using both the OpenGL and software rendering
backends.

Fixes b/132812775
Fixes flutter/flutter#35410

This exposes the `Settings::leak_vm` flag to custom embedders. All embedder
unit-tests now shut down the VM on the shutdown of the last engine in the
process. The mechanics of VM shutdown are already tested in the Shell unit-tests
harness in the DartLifecycleUnittests set of of assertions. This just exposes
that functionality to custom embedders. Since it is part of the public stable
API, I also switched the name of the field to be something less snarky than the
field in private shell settings.

embedder.h is a C API, so has no namespace, and only uses 'Flutter' as a
prefix for most symbol names. This creates potential collisions with
other code; for instance, FlutterEngine is the name of a type in
embedder.h, but also an ObjC class in the iOS Flutter API.

This adds a macro that can be set to prefix symbol names, allowing
clients (notably, the macOS embedding) to adjust the names used by the
embedding API internally without breaking ABI or API compatibility for
the standard engine build.

Currently the macro is only applied to FlutterEngine, since that's the
symbol that is currently at issue, but it can be expanded to other
symbols in the future.

Declare a copy of the enable_bitcode flag within the Flutter build scripts for use in Fuchsia builds (#10003)

enable_bitcode is defined in build/toolchain/clang.gni, which exists in the
Flutter buildroot but not in the Fuchsia source tree.

Debug builds log invalid file errors on launch of anything using the
embedding API due to an unconditional use of assets_dir, even though
only one of assets_dir or assets_path needs to be set (and the embedding
API currently uses the latter). This checks that the FD has been set
before trying to use it to create an asset resolver.

Also eliminates a duplicate code path in embedder.cc, where it was
calling RunConfiguration::InferFromSettings, then running exactly the
same asset manager creation code again locally.

Started adding the engine hash to Flutter.framework's Info.plist.

This patch reworks image decompression and collection in the following ways
because of misbehavior in the described edge cases.

The current flow for realizing a texture on the GPU from a blob of compressed
bytes is to first pass it to the IO thread for image decompression and then
upload to the GPU. The handle to the texture on the GPU is then passed back to
the UI thread so that it can be included in subsequent layer trees for
rendering. The GPU contexts on the Render & IO threads are in the same
sharegroup so the texture ends up being visible to the Render Thread context
during rendering. This works fine and does not block the UI thread. All
references to the image are owned on UI thread by Dart objects. When the final
reference to the image is dropped, the texture cannot be collected on the UI
thread (because it has not GPU context). Instead, it must be passed to either
the GPU or IO threads. The GPU thread is usually in the middle of a frame
workload so we redirect the same to the IO thread for eventual collection. While
texture collections are usually (comparatively) fast, texture decompression and
upload are slow (order of magnitude of frame intervals).

For application that end up creating (by not necessarily using) numerous large
textures in straight-line execution, it could be the case that texture
collection tasks are pending on the IO task runner after all the image
decompressions (and upload) are done. Put simply, the collection of the first
image could be waiting for the decompression and upload of the last image in the
queue.

This is exacerbated by two other hacks added to workaround unrelated issues.
* First, creating a codec with a single image frame immediately kicks of
  decompression and upload of that frame image (even if the frame was never
  request from the codec). This hack was added because we wanted to get rid of
  the compressed image allocation ASAP. The expectation was codecs would only be
  created with the sole purpose of getting the decompressed image bytes.
  However, for applications that only create codecs to get image sizes (but
  never actually decompress the same), we would end up replacing the compressed
  image allocation with a larger allocation (device resident no less) for no
  obvious use. This issue is particularly insidious when you consider that the
  codec is usually asked for the native image size first before the frame is
  requested at a smaller size (usually using a new codec with same data but new
  targetsize). This would cause the creation of a whole extra texture (at 1:1)
  when the caller was trying to “optimize” for memory use by requesting a
  texture of a smaller size.
* Second, all image collections we delayed in by the unref queue by 250ms
  because of observations that the calling thread (the UI thread) was being
  descheduled unnecessarily when a task with a timeout of zero was posted from
  the same (recall that a task has to be posted to the IO thread for the
  collection of that texture). 250ms is multiple frame intervals worth of
  potentially unnecessary textures.

The net result of these issues is that we may end up creating textures when all
that the application needs is to ask it’s codec for details about the same (but
not necessarily access its bytes). Texture collection could also be delayed
behind other jobs to decompress the textures on the IO thread. Also, all texture
collections are delayed for an arbitrary amount of time.

These issues cause applications to be susceptible to OOM situations. These
situations manifest in various ways. Host memory exhaustion causes the usual OOM
issues. Device memory exhaustion seems to manifest in different ways on iOS and
Android. On Android, allocation of a new texture seems to be causing an
assertion (in the driver). On iOS, the call hangs (presumably waiting for
another thread to release textures which we won’t do because those tasks are
blocked behind the current task completing).

To address peak memory usage, the following changes have been made:
* Image decompression and upload/collection no longer happen on the same thread.
  All image decompression will now be handled on a workqueue. The number of
  worker threads in this workqueue is equal to the number of processors on the
  device. These threads have a lower priority that either the UI or Render
  threads. These workers are shared between all Flutter applications in the
  process.
* Both the images and their codec now report the correct allocation size to Dart
  for GC purposes. The Dart VM uses this to pick objects for collection. Earlier
  the image allocation was assumed to 32bpp with no mipmapping overhead
  reported. Now, the correct image size is reported and the mipmapping overhead
  is accounted for. Image codec sizes were not reported to the VM earlier and
  now are. Expect “External” VM allocations to be higher than previously
  reported and the numbers in Observatory to line up more closely with actual
  memory usage (device and host).
* Decoding images to a specific size used to decode to 1:1 before performing a
  resize to the correct dimensions before texture upload. This has now been
  reworked so that images are first decompressed to a smaller size supported
  natively by the codec before final resizing to the requested target size. The
  intermediate copy is now smaller and more promptly collected. Resizing also
  happens on the workqueue worker.
* The drain interval of the unref queue is now sub-frame-interval. I am hesitant
  to remove the delay entirely because I have not been able to instrument the
  performance overhead of the same. That is next on my list. But now, multiple
  frame intervals worth of textures no longer stick around.

The following issues have been addressed:
* https://github.com/flutter/flutter/issues/34070 Since this was the first usage
  of the concurrent message loops, the number of idle wakes were determined to
  be too high and this component has been rewritten to be simpler and not use
  the existing task runner and MessageLoopImpl interface.
* Image decoding had no tests. The new `ui_unittests` harness has been added
  that sets up a GPU test harness on the host using SwiftShader. Tests have been
  added for image decompression, upload and resizing.
* The device memory exhaustion in this benchmark has been addressed. That
  benchmark is still not viable for inclusion in any harness however because it
  creates 9 million codecs in straight-line execution. Because these codecs are
  destroyed in the microtask callbacks, these are referenced till those
  callbacks are executed. So now, instead of device memory exhaustion, this will
  lead to (slower) exhaustion of host memory. This is expected and working as
  intended.

This patch only addresses peak memory use and makes collection of unused images
and textures more prompt. It does NOT address memory use by images referenced
strongly by the application or framework.

Fixes https://github.com/flutter/flutter/issues/18852

This was disabled in https://github.com/flutter/engine/pull/6798 waiting for
a Dart SDK patch to land https://github.com/dart-lang/sdk/commit/e6d3a45b6a98ea36581ac375ec5cdd63dd829004
which has long since been addressed.

Applications can use an embedder API to obtain the isolate ID and then use it
in calls to the Dart service protocol.

Messages sent to the embedder host may be one-way messages with no response
handler.  If the host calls FlutterEngineSendPlatformMessageResponse on a
one-way message, then just delete the message response handle.

Also update the documentation to indicate that
FlutterEngineSendPlatformMessageResponse must be called for all messages.
Previously the docs implied that some FlutterPlatformMessage objects may
have a null response_handle.  The embedder will now set a response_handle for
every message (even if the sender does not expect a response).

Linux target builds for non-x86/x64 platforms were failing due to the
dependency on SwiftShader

Currently, all our host unit-tests that have rendering concerns use the software backend because of OpenGL ES availability and stability issues on the various platforms where we run host tests. Unfortunately, entire subsystems are disabled (and not tested) when rendering with the software backend. This patch pulls in SwiftShader and via pending patches in the buildroot, configures the host unit-tests to optionally use OpenGL ES in a stable manner without relying on the OpenGL drivers being present (and functional).

I have wired up the embedder test fixture in this patch to use the SwiftShader based OpenGL ES driver. I will update the shell and runtime unittests in a subsequent patch as well. The on and offscreen surfaces are configured as 1x1 pbuffer surface because we should be able to write pixel tests using OpenGL directly wihout having to deal with surfaces.

* Revert "[fuchsia] Fix alignment of Fuchsia/non-Fuchsia tracing (#9289)"

This reverts commit f80ac5f5.

* Revert "Align fuchsia and non-fuchsia tracing (#9199)"

This reverts commit 78265484.

Using it, a Flutter app can monitor missing frames in the release mode, and a custom Flutter runner (e.g., Fuchsia) can add a custom FrameRasterizedCallback.

Related issues:
https://github.com/flutter/flutter/issues/26154
https://github.com/flutter/flutter/issues/31444
https://github.com/flutter/flutter/issues/32447

Need review as soon as possible so we can merge this before the end of May to catch the milestone.

Tests added:
* NoNeedToReportTimingsByDefault
* NeedsReportTimingsIsSetWithCallback
* ReportTimingsIsCalled
* FrameRasterizedCallbackIsCalled
* FrameTimingSetsAndGetsProperly
* onReportTimings preserves callback zone
* FrameTiming.toString has the correct format

This will need a manual engine roll as the TestWindow defined in the framework needs to implement onReportTimings.

* Allow specifying both Dart and non-Dart fixtures in engine unittests.

This fixes numerous issues in the way in which fixtures were managed
in the engine unit-tests.

* Instead of only being able to specify Dart fixtures, unit-tests may specify
  non-Dart fixtures as well. These are simply copied over to the fixtures
  directory known to the unit-test at runtime.
* An issue where numerous Dart files could be given to the kernel snapshotter
  has been addressed. It was anticipated that such a (legal) invocation to the
  kernel snapshotter would produce a snapshot with the contents of all the Dart
  files added to the root library. This is incorrect and the behavior in this
  case is undefined.
* Dart files referenced by the main Dart file are correctly tracked via a
  depfile.
* The snapshotter arguments have been cleaned up to get rid of unused
  arguments (`—strong`) and  the use of the VM product mode argument has been
  corrected to no longer depend on the Flutter product mode.

Corects a bnuch of typeos throughout teh engien codebsae. Also makes
a couple minor Commonwealth -> US spelling adjustments for consistency
with the rest of Flutter's codebase.

Made use of `misspell` tool:
https://github.com/client9/misspell

Rather than hard-coding the type of incoming events to mouse, and
synthesizing a primary button press for kDown/kUp, expose device kind
and buttons in the API.

For backwards compatibility, if the type is not set, the old behavior is
used. If an embedder sets the type to mouse explicitly, however, they
must also set correct button information.

For the touch type, the API abstracts away the framework's internal
expectation that a button is set for touch down/move for simplicity.

Fixes flutter/flutter#32854

This member variable was added to three classes in #7807, but only
initialized to 0 in one of them. Initialize to 0 in the other two.

This will reduce executable size.