* Revert "Fix documentation build for window changes. (#21780)"

This reverts commit 931a0468.

* Revert "Migration to PlatformDispatcher and multi-window (#20496)"

This reverts commit 85b0031f.

* carrying code

* more changes for carrying the code

* rebase changes onto ios-screenshot tests

* adding screenshot capability to text_editing e2e test

* address some comments

* change enable flag for isUnitTestsScreenshotsAvailable

* addressing the reviewer comments

* change the dependency for path

* add to licencense file

* changing goldens commit no. the new commit has the screenshot goldens

* update readme file

* firefox tests needs LUCI changes

* change to release mode since screenshots were taken in release mode

* change window size

* some argument changes

* small comment change

* test the chrome linux tests again

* use roboto font instead of default font

* addressing reviewer comments

* change commit for goldens

* Fix documentation build for window changes.

* Add missing interfaces for web_ui

This is a PR for converting the dart:ui code in the engine to use a multi-window API. The goal here is to convert from the window singleton to an API that has the concept of multiple windows. Also, I'm matching up the new PlatformDispatcher class to talk directly to the PlatformConfiguration class in the engine. I'm not attempting to actually enable creating multiple windows here, just migrate to an API that has a concept of multiple windows. The multi-window API in this PR currently only ever creates one window.

The design doc for this change is here.

The major changes in this PR:

Move the platfom-specific attributes out of Window, and into the new PlatformDispatcher class that holds all of the platform state, so that the platform code need only update the configuration on this class.
Create FlutterView, FlutterWindow, and SingletonFlutterWindow classes to separate out the concepts of a view (of which there may be multiple in a window), a window (of which there may be multiple on a screen, and they host views), and a window where there is only ever expected to be one (this hosts the entire API of the former Window class, and will eventually be the type of the window singleton).
Next step after this PR lands:

Remove the Window class entirely (it is replaced by SingletonFlutterWindow). Some minor changes in the Framework are needed to switch to using SingletonFlutterWindow directly first.

The Window class still exists in this PR, but will be removed as soon as the framework is converted to point to the SingletonFlutterWindow class instead. They share the same API, just have different names (Window is currently a subclass of SingletonFlutterWindow). The intention is that the Window name will be freed up to use as a widget class name in the framework for managing windows. The singleton called window will remain, and keep the same API it has now.

* Move shader.dart into shaders directory
* Add Shader builder basic structure and decls
* rewrite drawVertices with ShaderBuilder
* Fix in parameters in fragment shader to use varying for webgl1

* fixing the autofill overlay problem (blue area for chrome)

* addression comments

This reverts commit 02324994.

* Fix metaState for Key events for lock modifiers

Adds a reference to RenderObject.describeSemanticsClip to
`SemanticsFlag.isHidden` and a hint that lets readers know that the
`SemanticsNode` rect is specified in local coordinates.

* web: implement frame timings

* re-enable CanvasKit path ops test

* also test Path.combine

* Remove unnecessary `?`s from web_ui.

In https://dart-review.googlesource.com/c/sdk/+/163841, dart's flow
analysis is being changed so that an assignment like this:

    T? x = <non-nullable value>;

causes `x` to be immediately promoted to type `T`.  This exposed two
instances in which a variable was unnecessarily given a nullable type.
To avoid warnings, we need to fix these two types before
https://dart-review.googlesource.com/c/sdk/+/163841 can land.

* enable ios safari screenshot tests

* this is the value used for screenshots in the repo.

* change revision

* fix the error made in the gaps

* do not try to fetch on LUCI

* lunix luci migth break existing prs. only skip fetching for mac

* add a placeholder tests for shadow golden test

* try to use iPhone 11 Pro on LUCI

* change the scale and the smoke test image

* add unmerged goldens PR to tests all the screenshots. will be removed later

* change the goldens lock back to flutter/goldens

* change wrong comment on screenshot tests block

* address reviewer comments

* change the commit number for goldens file

* skip canvas blend mode tests

* debugging LUCI error

* debugging LUCI error printing directory contents

* skip one test, remove the debug logs

* change the revision number to include the correct chrome files

Revert "Revert "Adds fuchsia node roles to accessibility bridge updates. (#20385)" (#20936)" (#21367)

This reverts commit 96efe392.

* Avoid sending a 0 DPR to framework

* check width and height as well

This reverts commit cdc631c4.

* isCloneOf for Image

* Update docs, add missing impl

* web: make a few variables non-null

Allows for reference counting of images before disposal.

This will allow multiple callers to hold a reference to an image and dispose of their reference without disposing the underlying image until all handles have been disposed.

This will be used by the framework to help resolve some of the kludge I was trying to introduce in flutter/flutter#64582

for Android and iOS and remove offset from scenario_app test for iOS and Android.

* creating test result directory. adding a prepare method to test runner

* addressing reviewer comments

Registering the service worker immediately after the documented has loaded may cause SW initialization to compete with framework initialization. It was recommended to us that we defer the service worker setup until after the framework is done with setup, which should be sometime after the first frame.

To implement this, the binding will dispatch a platform message on startup. This can be listened for in the html document
#66066

* Make SkCanvas types @anonymous; reduce logging noise

* make SkParagraphBuilderNamespace anonymous

* make SkParagraphStyle anonymous