Additionally create "_next" permutations for all of the test binaries
on Fuchsia, in order to test both code-paths.

Using the #define follow-up CLs can also create a flutter_runner_next
binary that does not contain any legacy integration code.

BUG: 53847

Choose a child more likely to remain stable from frame to frame as the target to cache in the OpacityLayer.

This reverts commit a7a25d3b and relands our reland https://github.com/flutter/engine/pull/17915.

Additionally, we fixed the cull rect logic in `OpacityLayer::Preroll` which is  the root cause of https://github.com/flutter/flutter/issues/56298. We've always had that root problem before but it did not trigger performance issues because we were using the OpacityLayer's `paint_bounds`, instead of its child's `paint_bounds` for preparing the layer raster cache. A correct handling of the cull rect should allow us to cull at any level.

It also turns out that our ios32 (iPhone4s) performacne can regress a lot
without snapping. My theory is that although the picture has a
fractional top left corner, many drawing operations inside the picture
have integral coordinations. In older hardwares, keeping those
coordinates integral seems to be performance critical.

To avoid flutter/flutter#41654, the snapping
will still be disabled if the matrix has non-scale-translation
transformations.

This reverts commit b5aedb30 and relands #17712.

Fixes flutter/flutter#53288 and flutter/flutter#41654.

Together with #17791, this reland addresses some of Jim's concerns in the original PR #17712.

The major part of this PR is still the same as the original PR, and the performance / golden image impacts should be the same.

This avoids the possible matrix mismatch between RasterCache::Get and
RasterCacheResult::draw. See
https://github.com/flutter/engine/pull/17790 for an example that tries
to fix an earlier mismatch.

This reverts commit 99f8d007.

I found some problems. Will revise and reland later, and put more details about the problems in the new PR.

TBR: @chinmaygarde @flar 

This fixes https://github.com/flutter/flutter/issues/53288 and https://github.com/flutter/flutter/issues/41654. It removes the problematic `GetIntegralTransCTM`, but preserves the rect round-out in `RasterCacheResult::draw` for performance considerations: the average frame raster time doesn't change much but the worst frame raster time significantly regressed if rect round-out is removed. That's probably because a new shader needs to be compiled to draw raster cache with fractional offsets.

Revert "Try rasterizing images and layers only once , even when their rasterization fails. Further enforce the same access threshold on layers as on Pictures. Previously layers would always be cached. The latter is a semantic change. (#16545)" (#16889)

This caused regression in several benchmarks, including:
animated_placeholder_perf. Regression tracked in
https://github.com/flutter/flutter/issues/51776.

This reverts commit 01a52b99.

Try rasterizing images and layers only once, even when their rasterization fails. Further enforce the same access threshold on layers as on Pictures. Previously layers would always be cached. The latter is a semantic change. (#16545)

If Rasterization fails, i.e. image.is_valid() is false, the cache might try rasterizing the image again on the next frame. Not only is this wasteful put might also prevent other pictures to be cached within the current frame budget.

RasterCache::Get() methods were not updating the RasterCache::Entry
access_count and used_this_frame fields, as is done in
RasterCache::Prepare(). This can result in onscreen images being evicted
from the cache as new entries are created (e.g. as new elements scroll
onscreen).

This is a duplicate of flutter/engine#13360 with the test switched to use the software backend instead of the GL backend.

After some debugging and testing on another GL embedder I think the issue with the test is some bug having to do with the GL implementation in the test harness specifically. 

Fixes flutter/flutter#38903

This caused EmbedderTest.VerifyB143464703 to fail after merging into
master.

```
../../flutter/shell/platform/embedder/tests/embedder_unittests.cc:3111: Failure
Value of: ImageMatchesFixture("verifyb143464703.png", renderered_scene)
  Actual: false
Expected: true
[  FAILED  ] EmbedderTest.VerifyB143464703 (2507 ms)
```

This reverts commit 3ad3bc76.

Previously the cache was disabled on whether or not PlatformViews were
globally enabled. Instead track their existence in the view hierarchy
and only disable RasterCache if a PlatformView is actually present.

This follows our namespace change from shell to flutter: https://github.com/flutter/engine/pull/8520.

Reland ""Add support for trace counters with variable arguments and instrument the raster cache." (#8145)

This reverts commit bc901324 and fixes the
discovered on Windows builds.

Revert "Add support for trace counters with variable arguments and instrument the raster cache. (#8094)" (#8122)

This reverts commit 2a0d3542.

This decreases worst_frame_rasterizer_time_millis from 30ms to 10ms when
we enabled picture raster cache in tiles_scroll (i.e., lower the
threshold from 10 to 5).

* Revert "Revert "Allow raster caching any layer subtree (#6442)" (#6506)"

This reverts commit c6e6da51.

* Use raw pointer for RasterCacheKey

So we won't depend on whether it's a std::unique_ptr or std::shared_ptr.

Reverts flutter/engine#6442

container_layer.h file is not synced which broke the bots

We first test this with OpacityLayer. This test alone (without retained rendering) should have ~30% speedup as we'll have fewer render target switches by snapshoting in the Preroll instead of saveLayer in the Paint.

In my local flutter_gallery transition perf tests, the average frame time drops from ~16ms to ~12ms.

https://github.com/flutter/flutter/issues/21756

It should be sufficient to provide the matrix to preroll.

Fixes
1. https://github.com/flutter/flutter/issues/12148
2. most part of https://github.com/flutter/flutter/issues/17731 except some tiny AA diffs.

* Re-land "Support multiple shells in a single process. (#4932)"

This reverts commit 723c7d01.

This reverts commit a3327bff.

This reverts commit 9199b40f.

This reverts commit 6baff4c8.

* Support multiple shells in a single process.

The Flutter Engine currently works by initializing a singleton shell
instance. This shell has to be created on the platform thread. The shell
is responsible for creating the 3 main threads used by Flutter (UI, IO,
GPU) as well as initializing the Dart VM. The shell, references to task
runners of the main threads as well as all snapshots used for VM
initialization are stored in singleton objects. The Flutter shell only
creates the threads, rasterizers, contexts, etc. to fully support a
single Flutter application. Current support for multiple Flutter
applications is achieved by making multiple applications share the same
resources (via the platform views mechanism).

This scheme has the following limitations:

* The shell is a singleton and there is no way to tear it down. Once you
  run a Flutter application in a process, all resources managed by it
  will remain referenced till process termination.
* The threads on which the shell performs its operations are all
  singletons. These threads are never torn down and multiple Flutter
  applications (if present) have to compete with one another on these
  threads.
* Resources referenced by the Dart VM are leaked because the VM isn't
  shutdown even when there are no more Flutter views.
* The shell as a target does not compile on Fuchsia. The Fuchsia content
  handler uses specific dependencies of the shell to rebuild all the
  shell dependencies on its own. This leads to differences in frame
  scheduling, VM setup, service protocol endpoint setup, tracing, etc..
  Fuchsia is very much a second class citizen in this world.
* Since threads and message loops are managed by the engine, the engine
  has to know about threading and platform message loop interop on each
  supported platform.

Specific updates in this patch:

* The shell is no longer a singleton and the embedder holds the unique
  reference to the shell.
* Shell setup and teardown is deterministic.
* Threads are no longer managed by the shell. Instead, the shell is
  given a task runner configuration by the embedder.
* Since the shell does not own its threads, the embedder can control
  threads and the message loops operating on these threads. The shell is
  only given references to the task runners that execute tasks on these
  threads.
* The shell only needs task runner references. These references can be
  to the same task runner. So, if the embedder thinks that a particular
  Flutter application would not need all the threads, it can pass
  references to the same task runner. This effectively makes Flutter
  application run in single threaded mode. There are some places in the
  shell that make synchronous calls, these sites have been updated to
  ensure that they don’t deadlock.
* The test runner and the headless Dart code runner are now Flutter
  applications that are effectively single threaded (since they don’t
  have rendering concerns of big-boy Flutter application).
* The embedder has to guarantee that the threads and outlive the shell.
  It is easy for the embedder to make that guarantee because shell
  termination is deterministic.
* The embedder can create as many shell as it wants. Typically it
  creates a shell per Flutter application with its own task runner
  configuration. Most embedders obtain these task runners from threads
  dedicated to the shell. But, it is entirely possible that the embedder
  can obtain these task runners from a thread pool.
* There can only be one Dart VM in the process. The numerous shell
  interact with one another to manage the VM lifecycle. Once the last
  shell goes away, the VM does as well and hence all resources
  associated with the VM are collected.
* The shell as a target can now compile and run on Fuchsia. The current
  content handler has been removed from the Flutter engine source tree
  and a new implementation has been written that uses the new shell
  target.
* Isolate management has been significantly overhauled. There are no
  owning references to Dart isolates within the shell. The VM owns the
  only strong reference to the Dart isolate. The isolate that has window
  bindings is now called the root isolate. Child isolates can now be
  created from the root isolate and their bindings and thread
  configurations are now inherited from the root isolate.
* Terminating the shell terminates its root isolates as well as all the
  isolates spawned by this isolate. This is necessary be shell shutdown
  is deterministic and the embedder is free to collect the threads on
  which the isolates execute their tasks (and listen for mircrotasks
  flushes on).
* Launching the root isolate is now significantly overhauled. The shell
  side (non-owning) reference to an isolate is now a little state
  machine and illegal state transitions should be impossible (barring
  construction issues). This is the only way to manage Dart isolates in
  the shell (the shell does not use the C API is dart_api.h anymore).
* Once an isolate is launched, it must be prepared (and hence move to
  the ready phase) by associating a snapshot with the same. This
  snapshot can either be a precompiled snapshot, kernel snapshot, script
  snapshot or source file. Depending on the kind of data specified as a
  snapshot as well as the capabilities of the VM running in the process,
  isolate preparation can fail preparation with the right message.
* Asset management has been significantly overhauled. All asset
  resolution goes through an abstract asset resolver interface. An asset
  manager implements this interface and manages one or more child asset
  resolvers. These asset resolvers typically resolve assets from
  directories, ZIP files (legacy FLX assets if provided), APK bundles,
  FDIO namespaces, etc…
* Each launch of the shell requires a separate and fully configured
  asset resolver. This is necessary because launching isolates for the
  engine may require resolving snapshots as assets from the asset
  resolver. Asset resolvers can be shared by multiple launch instances
  in multiple shells and need to be thread safe.
* References to the command line object have been removed from the
  shell. Instead, the shell only takes a settings object that may be
  configured from the command line. This makes it easy for embedders and
  platforms that don’t have a command line (Fuchsia) to configure the
  shell. Consequently, there is only one spot where the various switches
  are read from the command line (by the embedder and not the shell) to
  form the settings object.
* All platform now respect the log tag (this was done only by Android
  till now) and each shell instance have its own log tag. This makes
  logs from multiple Flutter application in the same process (mainly
  Fuchsia) more easily decipherable.
* The per shell IO task runner now has a new component that is
  unfortunately named the IOManager. This component manages the IO
  GrContext (used for asynchronous texture uploads) that cooperates with
  the GrContext on the GPU task runner associated with the shell. The
  IOManager is also responsible for flushing tasks that collect Skia
  objects that reference GPU resources during deterministic shell
  shutdown.
* The embedder now has to be careful to only enable Blink on a single
  instance of the shell. Launching the legacy text layout and rendering
  engine multiple times is will trip assertions. The entirety of this
  runtime has been separated out into a separate object and can be
  removed in one go when the migration to libtxt is complete.
* There is a new test target for the various C++ objects that the shell
  uses to interact with the Dart VM (the shell no longer use the C API
  in dart_api.h). This allows engine developers to test VM/Isolate
  initialization and teardown without having the setup a full shell
  instance.
* There is a new test target for the testing a single shell instances
  without having to configure and launch an entire VM and associated
  root isolate.
* Mac, Linux & Windows used to have different target that created the
  flutter_tester referenced by the tool. This has now been converted
  into a single target that compiles on all platforms.
* WeakPointers vended by the fml::WeakPtrFactory(notice the difference
  between the same class in the fxl namespace) add threading checks on
  each use. This is enabled by getting rid of the “re-origination”
  feature of the WeakPtrFactory in the fxl namespace. The side effect of
  this is that all non-thread safe components have to be created, used
  and destroyed on the same thread. Numerous thread safety issues were
  caught by this extra assertion and have now been fixed.
  * Glossary of components that are only safe on a specific thread (and
    have the fml variants of the WeakPtrFactory):
    * Platform Thread: Shell
    * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator
    * GPU Thread: Rasterizer, Surface
    * IO Thread: IOManager

This patch was reviewed in smaller chunks in the following pull
requests. All comments from the pulls requests has been incorporated
into this patch:

* flutter/assets: https://github.com/flutter/engine/pull/4829
* flutter/common: https://github.com/flutter/engine/pull/4830
* flutter/content_handler: https://github.com/flutter/engine/pull/4831
* flutter/flow: https://github.com/flutter/engine/pull/4832
* flutter/fml: https://github.com/flutter/engine/pull/4833
* flutter/lib/snapshot: https://github.com/flutter/engine/pull/4834
* flutter/lib/ui: https://github.com/flutter/engine/pull/4835
* flutter/runtime: https://github.com/flutter/engine/pull/4836
* flutter/shell: https://github.com/flutter/engine/pull/4837
* flutter/synchronization: https://github.com/flutter/engine/pull/4838
* flutter/testing: https://github.com/flutter/engine/pull/4839

Plumb through Scenic display metrics to use during
Preroll.

Revert "Revert "Reland "Run Flutter on iOS and Android with color correct Skia (#3826)" (#3878)" (#3895)

This reverts commit 1db18a40.

This reverts commit 2d9155e1.

Fixes a regression with semitransparent images (flutter/flutter#11169)