Eliminates FLUTTER_NOLINT where they can be landed without triggering
lint failures.

Snapshots compiled with sound null-safety enabled require changes to the way in
which isolates are launched. Specifically, the `Dart_IsolateFlags::null_safety`
field needs to be known upfront. The value of this field can only be determined
once the kernel snapshot is available. This poses a problem in the engine
because the engine used to launch the isolate at shell initialization and only
need the kernel mappings later at isolate launch (when transitioning the root
isolate to the `DartIsolate::Phase::Running` phase). This patch delays launch of
the isolate on the UI task runner till a kernel mapping is available. The side
effects of this delay (callers no longer having access to the non-running
isolate handle) have been addressed in this patch. The DartIsolate API has also
been amended to hide the method that could return a non-running isolate to the
caller.  Instead, it has been replaced with a method that requires a valid
isolate configuration that returns a running root isolate. The isolate will be
launched by asking the isolate configuration for its null-safety
characteristics.

A side effect of enabling null-safety is that Dart APIs that work with legacy
types will now terminate the process if used with an isolate that has sound
null-safety enabled. These APIs may no longer be used in the engine. This
primarily affects the Dart Convertors in Tonic that convert certain C++ objects
into the Dart counterparts. All known Dart Converters have been updated to
convert C++ objects to non-nullable Dart types inferred using type traits of the
corresponding C++ object. The few spots in the engine that used the old Dart
APIs directly have been manually updated. To ensure that no usage of the legacy
APIs remain in the engine (as these would cause runtime process terminations),
the legacy APIs were prefixed with the `DART_LEGACY_API` macro and the macro
defined to `[[deprecated]]` in all engine translation units. While the engine
now primarily works with non-nullable Dart types, callers can still use
`Dart_TypeToNonNullableType` to acquire nullable types for use directly or with
Tonic. One use case that is not addressed with the Tonic Dart Convertors is the
creation of non-nullable lists of nullable types. This hasn’t come up so far in
the engine.

A minor related change is reworking tonic to define a single library target.
This allows the various tonic subsystems to depend on one another. Primarily,
this is used to make the Dart convertors use the logging utilities. This now
allows errors to be more descriptive as the presence of error handles is caught
(and logged) earlier.

Fixes https://github.com/flutter/flutter/issues/59879

Cleans up header order/grouping for consistency: associated header, C/C++ system/standard library headers, library headers, platform-specific #includes.

Adds <cstring> where strlen, memcpy are being used: there are a bunch of places we use them transitively.

Applies linter-required cleanups. Disables linter on one file due to included RapidJson header. See https://github.com/flutter/flutter/issues/65676

This patch does not cover flutter/shell/platform/darwin. There's a separate, slightly more intensive cleanup for those in progress.

* Use hint freed specifically for image disposal

Fixes https://github.com/flutter/flutter/issues/59109

Make the test harness reusable for other tests that want to launch a Dart VM

These add no value to engine developers anymore and are not visible to external
users because of the low log severity.

Isolate data may need to be deleted on the same thread where it was allocated.
In particular, the task observer set up in the UIDartState ctor must be removed
from the same message loop where it was added.

The engine had been using the same DartIsolate object as the root isolate data
and as the isolate group data.  This object would be deleted when the isolate
group was shut down.  However, group shutdown may occur on a thread associated
with a secondary isolate.  When this happens, cleanup of any state tied to the
root isolate's thread will fail.

This change adds a DartIsolateGroupData object holding state that is common
among all isolates in a group.  DartIsolateGroupData can be deleted on any
thread.

See https://github.com/flutter/flutter/issues/45578

* Revert "Revert "Provide dart vm initalize isolate callback so that children isolates belong to parent's isolate group. (#9888)" (#12327)"

* Ensure that when isolate shuts down it calls isolate_data, rather than isolage_group_data callback.

Put `Picture.toImage` back on the GPU thread.  Left the unit tests intact.

Remove dead shared snapshot arguments to Dart_CreateIsolateGroup.

6a65ea9cad4b [vm] Remove shared snapshot and reused instructions features.
db8370e36147 [gardening] Fix frontend-server dartdevc windows test.
4601bd7bffea Modified supertype check error message to be more descriptive.
0449905e2de6 [CFE] Add a serialization-and-unserialization step to strong test
c8b903c2f94f Update CHANGELOG.md
2a12a13d9684 [Test] Skips emit_aot_size_info_flag_test on crossword.
b26127fe01a5 [cfe] Add reachability test skeleton

Obtaining the SkiaUnrefQueue through the IOManager is unsafe because
UIDartState has a weak pointer to the IOManager that can not be dereferenced
on the UI thread.

This reverts commit e96c7404.

* Update secondary-isolate-launch test to verify that secondary isolate gets shutdown before root isolate exits.

* ci/format.sh

We will end up creating fewer threads in tests.

Made Picture::toImage happen on the IO thread with no need for a surface.

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.

The callbacks can be wired in via the Settings object. Both runtime and shell unit-tests have been patched to test this.

The failing tests were depending on the old assumption that the VM would never
shutdown.

Some components in the Flutter engine were derived from the forked blink codebase. While the forked components have either been removed or rewritten, the use of the blink namespace has mostly (and inconsistently) remained. This renames the blink namesapce to flutter for consistency. There are no functional changes in this patch.

Revert "Revert "Separate the data required to bootstrap the VM into its own class. (#8397)" (#8406)" (#8414)

This reverts commit f7b4903d.

This reverts commit c9916474.

When attempting to shutdown and subsequently restart the VM, having the
VM own this data introduces lifecycle issues due to circular references.

Previously, only the most basic tests were run in AOT mode.

* Test profile build and unit tests

* update googletest, skip JIT tests on non-debug builds

This reverts commit 0d6ff166.

The shell was already designed to cleanly shut down the VM but it couldnt
earlier as |Dart_Initialize| could never be called after a |Dart_Cleanup|. This
meant that shutting down an engine instance could not shut down the VM to save
memory because newly created engines in the process after that point couldn't
restart the VM. There can only be one VM running in a process at a time.

This patch separate the previous DartVM object into one that references a
running instance of the DartVM and a set of immutable dependencies that
components can reference even as the VM is shutting down.

Unit tests have been added to assert that non-overlapping engine launches use
difference VM instances.

* Make IOManager own resource context