Bug: https://github.com/flutter/flutter/issues/17833

* Roll engine to 56139397e6ae1257bdabd1ef79ff7aca96c67d4.6

Changes since last roll:
```
56139397e Roll src/third_party/skia 7ba1d64f0706..5f0726b01019 (12 commits) (#6104)
47a1ce0e6 Allow embedders to set the root surface transformation. (#6085)
```

* Roll engine to f3ff83a5db71262d240aa5337a2a9a22c73c4749. (dart roll).

* Add const

* Add ignore analyzer prefer_const_constructors_in_immutables

Update CONTRIBUTING.md to suggest Android Studio and fix Mac command to install android-platform-tools. (#19537)

https://github.com/flutter/engine/compare/af42b6dc95bd...56bad48ab2ed

git log af42b6dc95bd..56bad48ab2ed --no-merges --oneline
56bad48ab expose bold text flag in accessibility features for iOS (flutter/engine#6072)
ad4e87d07 Convert synthesized Android motion events to long and not to int. (flutter/engine#6103)
f05b08b7b Roll src/third_party/skia f125111ca733..7ba1d64f0706 (18 commits) (flutter/engine#6102)
eb9738610 Roll src/third_party/skia 0fdc53f9ffc6..f125111ca733 (10 commits) (flutter/engine#6100)
06b8fa4ed Roll src/third_party/skia dd04bec39cea..0fdc53f9ffc6 (13 commits) (flutter/engine#6098)
bf078042d Roll ICU to c56c671998902fcc4fc9ace88c83daa99f980793 (flutter/engine#6097)
c867305c3 Unconditionally set resource id to empty string (flutter/engine#6096)
b4b1d0578 Roll src/third_party/skia e00fe30b8fe7..dd04bec39cea (4 commits) (flutter/engine#6095)
8694036a6 Roll src/third_party/skia 420696961c8c..e00fe30b8fe7 (1 commits) (flutter/engine#6094)


The AutoRoll server is located here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

* Fix coverage collection crash

Based on Jason's patch in https://github.com/flutter/flutter/pull/19546/

This is more or less the same but I tried to avoid using `dynamic`.

* Improve argument and variable names in flutter_platform

* Don't bother with reduce, since the order is guaranteed.

* Remove workaround for dart-lang/dartdoc#1125

* Update update_icons.dart for optional const and to remove markup stripping workaround

Apparently Gradle leaks memory and it's causing failures.

* Don't time out if process terminates when told to stop but response was not processed

While trying to reproduce #20822 I found a condition where the app may quit before the `app.stop` response is received but this code (which is called in integration test teardown) would sit around waiting and time out. With this change, the process exit is considered a valid response to the stop request.

* Add process exit to log for better errors in failures

This log can be turned on for debugging but is also dumped when a test fails (in certain conditions). With this in the log, it'll be clear if the timeout is because we're waiting for an event but the process quit.

Fixes https://github.com/flutter/flutter/issues/14578.

This re-lands commit c594696f.

The original PR was breaking the integration test as while the
gesture was active the AndroidView's parent widget got rebuilt which
disposed the _AndroidViewGestureRecognizer and dropped pointer events
from that point on.

This change adds a unit test that reproduces the failure case, and
fixes it by not rebuilding the _AndroidViewGestureRecognizer if the
list of gesture recognizers did not change.

ANDROID_HOME should be coming from the env, and it wasn't: it was being set in the script.

This reverts commit c594696f.

Pointer events are dispatched to the Android view only if it won
Flutter's gesture arena for the pointer.
Specific gestures that should be dispatched to the android view can be
specified with the gestureRecognizers parameter.

Add a countdown timer picker as part of the Cupertino date picker.

Note that such tests already exist for RaisedButton and MaterialButton

This allows to pass construction parameters for the embedded Android
view from the Dart side.

* Few readme fixes

* Fix link

* Make casing consistent

* Unskip expression evaluation integration tests for non-Windows

* Add additional into to skip comments

* Add missing import

Auto-roller completed checks. Merging.

Auto-roller completed checks. Merging.

This adds ".pub-cache" to the list of directories to ignore when checking for dependence upon dart:test, since when people install a downloadable package, their pub cache is in the flutter directory.

Also, I centralized the ANSI "red line" so that they would all use the same final string.

This allows developers to control the clipBehavior of those buttons.

This updates the test to match the engine API change introduced in:
https://github.com/flutter/engine/pull/6081

This also rolls the engine, the roll includes only the relevant engine commit:
```
091492601 Allow passing extra creation parameters for embedded Android views. (#6081)
```

Auto-roller completed checks. Merging.

Updating a few things on the README page. It needs more work.

Was marked as flaky as that's our policy for assing new device lab
tests. It's been consistently green so marking as non flaky.