* Serialize compilation requests.

* update tests for TextStyle changes in engine

* roll engine, support Foreground on TextStyle

* roll to TextStyle.foreground

* add tests, update docs, fixes from tests

* add golden tests

* stroke + gradient

* update goldens hash

* Use centered widget

* fix typo

* Disable golden tests until Linux generated files are available

* update goldens

* Roll to 549c855e89341b97436b3417542fc8f997492df7

* Clean up return void - see https://github.com/dart-lang/sdk/issues/33218

* Add doc example to addLocalHistoryEntry in LocalHistoryRoute (#9392)

The new matcher package deprecates isInstanceOf which seems eggregious.

Fix test.

This makes the buildbot green again.

* Add docs to Opacity recommending AnimatedOpacity for opacity animations (#15464)

Reported for the hello_world compile benchmark in devicelab for now.

This adds an HSLColor class which uses a perceptual color space based upon human perception of colored light (as opposed to HSV, which is based on pigment colors).

You can see the difference in the color spaces here: https://en.wikipedia.org/wiki/HSL_and_HSV

I also added a "within" matcher for both HSLColor and HSVColor that will check if the (floating point) color components are within a certain error.

And tests.

* Roll the engine.

This engine includes a VM that defaults to sync-async.

flutter/engine@c8eeee4 Roll the Dart VM.

Seems like VS Code may have started using lowercase extension folders recently (our identifier is `Dart-Code.flutter` but now the folder is named `dart-code.flutter`), so this makes the check not sensitive to casing.

Also reuse extension identifier for download link

... and make sure they fail if they can't report the size.

This reverts commit 77508722.

We have many hidden children because of iOS accessibility (see also #18410).

For example, in the tile screen of complex_layout app, there could be up to 20 children being painted without this PR. With this PR, only 12 get painted.

This should improve the performance of FL-53 by 40%.

Add flutter tool support for creating app-specific VM snapshots.

Fixes #10826.

Also in this PR: If you focus a text field, scroll it out of view and then start typing it will scroll back into view.