* Automatic focus highlight mode for FocusManager

This re-lands the highlight mode change.

* Review Changes

This reverts commit 5e7beaf7.

* WIP

* trying out different numbers

* apply intrinsic width and height

* update

* update behavior

* documentation

* wip

* fix tests

* constants

* respect theme

* respect theme

* add new test

* add new test

* update

* review

* update golden commit hash

* WIP on web plugin registry

* WIP on registering plugins

* WIP on web plugin registration

* Only generate `package:flutter_web_plugins` imports if plugins are
defined

* Add parsing test

* Add documentation

* Fix analyzer warnings

* add license headers

* Add tests for package:flutter_web_plugins

* Run `flutter update-packages --force-upgrade`

* Fix analyzer errors

* Fix analyzer error in test

* Update copyright and remove flutter SDK constraints

* Enable tests since engine has rolled

* add flutter_web_plugins tests to bots

* Create an empty .packages file for WebFs test

fix sliverfixedextent with sliverchildbuilderdelegate does not correct calculate max scroll extent (#39142)

One of our linux/android Moto G4 has alerts (emergency, amber, etc.)
turned on. That's probably the cause of the flakiness. I've turned it
off.

Let's mark this as non-flaky and see if it's fixed. If not, I'll move it
to mac/android and see if that fixes the flakiness.

I think the most important thing to do right now is to mark it as
non-flaky so those who really break the test could get a notification.

This changes the behavior of text fields, Material buttons, and Chips so that if they are disabled they lose focus. Before this change, it was possible to disable a control and then use focus traversal to reach it anyhow, and in the case of text fields, enter text into a disabled field.

Fixes #33985

e7f9ef6aa Roll src/third_party/skia 8203a180ea5d..94c66475560d (1 commits) (flutter/engine#11826) (#39713)


git@github.com:flutter/engine.git/compare/51a376d73ba1...e7f9ef6aa0b9

git log 51a376d73ba1..e7f9ef6aa0b9 --no-merges --oneline
2019-09-03 skia-flutter-autoroll@skia.org Roll src/third_party/skia 8203a180ea5d..94c66475560d (1 commits) (flutter/engine#11826)


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 garyq@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

51a376d73 [Windows] Update API for alternative Windows shell platform implementation (flutter/engine#11327) (#39710)


git@github.com:flutter/engine.git/compare/3deb8f5e45e1...51a376d73ba1

git log 3deb8f5e45e1..51a376d73ba1 --no-merges --oneline
2019-09-03 james@clarkezone.net [Windows] Update API for alternative Windows shell platform implementation (flutter/engine#11327)


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 garyq@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

3deb8f5e4 Roll fuchsia/sdk/core/linux-amd64 from 0qRbW... to a8wlq... (flutter/engine#11825) (#39709)


git@github.com:flutter/engine.git/compare/dcf5d6ab3447...3deb8f5e45e1

git log dcf5d6ab3447..3deb8f5e45e1 --no-merges --oneline
2019-09-02 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/linux-amd64 from 0qRbW... to a8wlq... (flutter/engine#11825)


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 garyq@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

The Current->A symlink in a framework shouldn't have a trailing slash;
some versions of codesigning consider the version with a trailing slash
unsignable.

git@github.com:flutter/engine.git/compare/d250375fa6bc...dcf5d6ab3447

git log d250375fa6bc..dcf5d6ab3447 --no-merges --oneline
2019-09-02 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/mac-amd64 from ApgEE... to pVy4h... (flutter/engine#11824)


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 garyq@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

Use the entire appBarTheme from the showSearch delegate for the search pages appBar theme, rather than just a select set of fields.

d250375fa Roll fuchsia/sdk/core/linux-amd64 from iV65h... to 0qRbW... (flutter/engine#11823) (#39682)


git@github.com:flutter/engine.git/compare/60406ad9fac9...d250375fa6bc

git log 60406ad9fac9..d250375fa6bc --no-merges --oneline
2019-09-02 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/linux-amd64 from iV65h... to 0qRbW... (flutter/engine#11823)


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 garyq@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/2baba33c8297...60406ad9fac9

git log 2baba33c8297..60406ad9fac9 --no-merges --oneline
2019-09-02 skia-flutter-autoroll@skia.org Roll fuchsia/sdk/core/mac-amd64 from AAphf... to ApgEE... (flutter/engine#11822)


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 garyq@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

2baba33c8 Roll src/third_party/skia 0a1e9efa392c..8203a180ea5d (4 commits) (flutter/engine#11821) (#39676)


git@github.com:flutter/engine.git/compare/62d880877362...2baba33c8297

git log 62d880877362..2baba33c8297 --no-merges --oneline
2019-09-02 skia-flutter-autoroll@skia.org Roll src/third_party/skia 0a1e9efa392c..8203a180ea5d (4 commits) (flutter/engine#11821)


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 garyq@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