* Revert "Add flow test fixtures and tests (#13986)"

This reverts commit 620f5281.

* Revert "Dynamically determine whether to use offscreen surface based on need (#13976)"

This reverts commit a86ef946.

Only use an offscreen surface on iOS if a layer which reads back from the destination surface, such as BackdropFilter, is present.

* DRAFT: adding support for enabling semantics on desktop

* Working solution for desktop.

* Refactoring class structure. Removing unrelated comments.

* Fixing enabling semantics from dom_renderer

* Adding unit tests.Fixing failing cases. More refactoring.

* more work on tests.

* Fixing licences

* addressing PR comments

The converters are still in a separate target that must be included manually. This allows targets that depend on FML but not Dart runtime not have to depend on the runtime.

Adds a test that includes this target and tests image decompression from assets. There is also a test for the standalone DartConvertor in shell_unittests but not in fml_unittests be cause FML uni-tests cannot yet launch a VM. I will work on adding fixtures for those.

* SkCanvas -> SkLayerCanvas

SkRecordingCanvas -> SkCanvas

* Move files

* WIP on canvas refactor

* Refactor CanvasKit backend

* fix tests

* update licenses

* Respond to PR comments

* Add fuchsia MessageLoopImpl; fix several tests

This ensures we rasterize into the canvas passed in as subclasses may reimplement AcquireFrame in different ways that don't utilize the canvas object passed in (such as Fuchsia's flutter_runner::CompositorContext).

* Implement basic text rendering support in CanvasKit backend

* Update licenses

* Address PR comments

This allows custom compositors to affect scene builder modifications made
to the platform view.

Fixes https://github.com/flutter/flutter/issues/44211
Fixes b/143612326

* Moves pointer event sanitizing to engine

* fix comment format

* fix formatting

* addressing comment

* fix format

* fix format

* addressing comment

This reverts commit f456423c.

This is being reverted because it caused flutter/flutter#45098
(images don't load on iOS).

* Move Path and PathMetrics into their own files. No delta
* update file list in licenses_flutter

* Implement ImageFilter.blur and BackdropFilter

* update licenses file

* Respond to review comments

This reverts commit 2dcfaaeb.

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

* Implement Path.computeMetrics in the CanvasKit backend

* Add license for path_metrics.dart

This reverts commit 618e6666.

Revert "Always use `IOSGLContextSwitch` to access EAGLContexts to prevent plugins from polluting Flutter's EAGLContext (#13314)" (#13753)

Always use `IOSGLContextSwitch` to access EAGLContexts to prevent plugins from polluting Flutter's EAGLContext (#13314)

Ensure that the device pixel ratio is taken into account with window metrics in physical pixels. (#13708)

This was originally patched in https://github.com/flutter/engine/pull/13193 but
the unit-tests were written under the mistaken assumption (that has been
documented already) that the Flutter window metrics used logical pixel
coordinates. That mistake has been corrected and additional tests to verify
rendering intent has been added.

Fixes https://github.com/flutter/flutter/issues/43906
Fixes https://b.corp.google.com/issues/143529469

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

This used to only be handled correctly for non-root layer backing stores. This
was mostly a side effect of the fact that we used recording canvases instead of
rendering directly into the backing store. We now use recording canvases
consistently.

Fixes b/143464703
Fixes https://github.com/flutter/flutter/issues/43732

Switch the MacOS Desktop embedder to using a thread configuration where the platform and render task runners are the same. (#13300)

Also creates a new test harness for the desktop embedder framework target and adds a test that launches a headless engine in this new thread configuration.

Fixes https://github.com/flutter/flutter/issues/17579

The FIDL service `fuchsia.intl.PropertyProvider` is a service that
the flutter runner can use to obtain information on system preferred
locales.

This change sends a platform message "setLocale" on the channel
"flutter/localization", based on the values provided by the above
mentioned FIDL service.

Credit: most of this was initially written by @kpozin; I ported it
to out-of-tree flutter engine.

Tested:

1. Compile and publish the unit tests package as shown in
   the script below.
2. In a Fuchsia repository (pointed to by `$FUCHSIA_DIR`), run
   `fx serve`
3. `fx shell run fuchsia-pkg://fuchsia.com/flutter_runner_tests#meta/flutter_runner_tests.cmx`

The script used to update the unit tests.

```bash

set -x

FLUTTER_ENGINE_DIR="${FLUTTER_ENGINE_DIR:-$HOME/fx/flutter/engine/src}"
readonly OUT_DIR="${FLUTTER_ENGINE_DIR}/out"

(
  cd ${FLUTTER_ENGINE_DIR}
  ./flutter/tools/gn --fuchsia --fuchsia-cpu x64 --unoptimized
  ninja -j 100 -C "${OUT_DIR}/fuchsia_debug_unopt_x64"
  cp "${OUT_DIR}/compile_commands.json" "${FLUTTER_ENGINE_DIR}"

  echo "Publishing the tests package"
  "${FLUTTER_ENGINE_DIR}/fuchsia/sdk/linux/tools/pm" publish \
    -a -r $FUCHSIA_DIR/out/release/amber-files \
    -f "${FLUTTER_ENGINE_DIR}/out/fuchsia_debug_unopt_x64/flutter_runner_tests-0.far"
)
```

SkiaUnrefQueue should be empty at destruction time.  If the queue is nonempty,
then there will be a pending drain task that will hold a reference to the
queue.  The queue can only be destructed after the drain completes and the
reference is dropped.

Drains must only be done on the queue's task runner thread, which may not be
the thread where the queue is destructed.

* Update CanvasKit to 0.7.0 and flesh out painting

This allows us to fix some bugs in the CanvasKit backend.

- Implement RRect where the radii are different
- Implement drawDRRect
- Implement ColorFilter
- Implement the correct `arcTo` for `arcToPoint`

* update licenses

* Respond to review comments

- Add TODO to avoid unnecessary conversions
- Don't set CanvasKit to default
- Fix licenses file

* Add ==, hashCode, and toString back to ColorFilter API

* Draw vertices to shared offscreen canvas on browsers that support OffscreenCanvas.
* Move gl rendering code to render_vertices.dart.
* Reuse shaders and program across calls.

Adds a task runner, and exposes API to allow application-level runloops to know when they need to next call the API to process engine events. Internally, sends null events to wake up the app runloop when new events are scheduled to ensure the wait time is updated accordingly.

Fixes #36420

Fixes https://github.com/flutter/flutter/issues/42704.