SliverAppBar - Configurable overscroll stretch with callback feature & FlexibleSpaceBar support (#42250)

* remove Source.behavior, fix bug in depfile invalidation

* more cleanup of assets

* Add skip

* address comments

* Update build_system.dart

Added tests for the new Android heading semantic flag to android_semantics_testing.

* Adding handling of TextInputClient.onConnectionClosed messages handling to Framework

* Adding more test cases for closing connection to editable_text_test

* fixing analyze error.

* Fixing analyze error in the test file

* Fixing comments on the new method

* Adding more closing connection examples.

* Indentation change

* Remove auto-add white space

* Changing the oncloseconnection behaviour to stop editing. Updating the tests

* Addressing PR comments. Added explicit log for method channnels to the tests. Added comments to the interfaces.

* add more documentation

* Wire enableFeedback parameter through MaterialButton, RawMaterialButton, and IconButton.
Co-Authored-By: Shi-Hao Hong <shihaohong@google.com>

This reverts commit 99cd4403.

This is being done to match the Material spec. It will likely break many visual diff tests.

git@github.com:flutter/engine.git/compare/44c9fab7b4d8...8ea19b1c76f6

git log 44c9fab7b4d8..8ea19b1c76f6 --no-merges --oneline
2019-10-31 skia-flutter-autoroll@skia.org Roll src/third_party/skia 549325c87e9d..809ec77893be (1 commits) (flutter/engine#13458)
2019-10-31 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/mac-amd64 from p7XYM... to JngMB... (flutter/engine#13456)
2019-10-31 iska.kaushik@gmail.com [fuchsia] [packaging] Prettify parent folder name (flutter/engine#13463)
2019-10-31 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/linux-amd64 from nhX22... to 866GG... (flutter/engine#13450)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC cbracken@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

This adds accessors for WidgetsBinding.instance.focusManager and WidgetsBinding.instance.focusManager.primaryFocus so that they can be more easily found in IDEs and accessed.

This adds a top level getter for WidgetsBinding.instance.focusManager.primaryFocus called primaryFocus, and a static accessor FocusManager.instance that returns WidgetsBinding.instance.focusManager.

git@github.com:flutter/engine.git/compare/73541c97b8b6...44c9fab7b4d8

git log 73541c97b8b6..44c9fab7b4d8 --no-merges --oneline
2019-10-31 bkonyi@google.com Roll src/third_party/dart d50c158d42..bbe2ac28c9 (19 commits)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC cbracken@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

git@github.com:flutter/engine.git/compare/7c80d62e89f6...73541c97b8b6

git log 7c80d62e89f6..73541c97b8b6 --no-merges --oneline
2019-10-31 iska.kaushik@gmail.com [recipe] Upload sky_engine to CIPD (flutter/engine#13464)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC cbracken@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

git@github.com:flutter/engine.git/compare/4b76fadbf438...7c80d62e89f6

git log 4b76fadbf438..7c80d62e89f6 --no-merges --oneline
2019-10-31 iska.kaushik@gmail.com CIPD needs the directory to be relative (flutter/engine#13461)
2019-10-31 1541038+josh-ksr@users.noreply.github.com Force orientation change when current orientation not allowed on iOS (flutter/engine#13170)
2019-10-31 jason-simmons@users.noreply.github.com Duplicate the directory fd in fml::VisitFiles (flutter/engine#13448)
2019-10-31 amirh@users.noreply.github.com Fix iOS crash when multiple platform views are in the scene (flutter/engine#13449)
2019-10-30 skia-flutter-autoroll@skia.org Roll src/third_party/skia 7df14d055703..549325c87e9d (11 commits) (flutter/engine#13447)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC cbracken@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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