Brings hello_world and flutter_gallery Android code in line with the
corresponding iOS code.

Also, I had a question about flutter_test matchers and our style guide
says that when I have a question I should update the docs so I did
that and then got a bit carried away.

See https://github.com/flutter/flutter/issues/9726; for some reason
the markdown in this file is getting misinterpreted.

Fixes #9757

Fixes https://github.com/flutter/flutter/issues/9342

* Revert "Revert "Don't try to resolve CocoaPods unless project has plugins" (#9719)"

This reverts commit f739e9e0.

* Remove channels integration test’s partial cocoapods artifacts

Fixes https://github.com/flutter/flutter/issues/7988

* Let printError print bold as well

* review notes

Fixes https://github.com/flutter/flutter/issues/8476

More detailed list of changes in this patch:

* Replaced the didTouch special logic with more generic logic that
  uses Activities instead. Now instead when you tap down the
  Scrollable calls `hold()` which begins a HoldScrollActivity which is
  a hybrid of DragStartDetails and IdleScrollActivity and can be
  canceled. When you let go, it gets canceled and that goes ballistic.

* Make DragGestureRecognizer more aggressive about grabbing pointers,
  otherwise a second pointer in a situation with competing horizontal
  and vertical recognizers always gets taken by the other one.

* Fixed the _GestureSemantics widget to call the "down" callbacks so
  that it follows the same pattern as "real" interactions.

* Added tests for the above.

* Added a hashCode to ScrollActivity.toString (and subclasses).

* Added a toString to ScrollDragController, and include it in
  DragScrollActivity's toString.

* s/coorindator/coordinator/

* Add a comment in DragStartDetails to distinguish it from the
  otherwise identical DragDownDetails, so we're not tempted to merge
  them.

* Don’t automatically pod setup if the user never did it

* fix/add test

* rename getters

* fix an issues with reloading when paused at a breakpoint

* update docs

Eliminates Gallery-specific hardcoding of app package and activity name
in the test.

Fixes breakage introduced with 1dc2d4eb
due to main activity class now being MainActivity.

If there is more than one action, then the AppBar should align the title to the
left according to
<https://material.io/guidelines/platforms/platform-adaptation.html#platform-adaptation-platform-recommendations>

* Populate PUB_ENVIRONMENT for initial pub get

* review comments

* change order

As required by
<https://material.io/guidelines/platforms/platform-adaptation.html#platform-adaptation-platform-recommendations>.

This splits the frame pipeline into two, beginFrame and drawFrame.

As part of making this change I added some debugging hooks that helped
debug the issues that came up:

 * I added debugPrintScheduleFrameStacks which prints a stack whenever
   a frame is actually scheduled, so you can see why frames are being
   scheduled.

 * I added some toString output to EditableText and RawKeyboardListener.

 * I added a scheduler_tester.dart library for scheduler library tests.

 * I changed the test framework to flush microtasks before pumping.

 * Some asserts that had the old string literal form were replaced by
   asserts with messages.

I also fixed a few subtle bugs that this uncovered:

 * setState() now calls `ensureVisualUpdate`, rather than
   `scheduleFrame`. This means that calling it from an
   AnimationController callback does not actually schedule an extra
   redundant frame as it used to.

 * I corrected some documentation.

* Adjust the defaults behaviour of scroll views.

Now, primary scroll views scroll by default. Others only scroll if necessary.

* apply suggested changes

* Revert "Document ScrollController (#9705)"

This reverts commit ff8609f2.

* Revert "Fix channels integration test (#9713)"

This reverts commit aace622d.

* Revert "Fix flutter view project's automated tests (#9712)"

This reverts commit 1a4bf9b6.

* Revert "Update hello_world_memory_test package name (#9704)"

This reverts commit ffa8483f.

* Revert "Increment the flutter package version (#9699)"

This reverts commit 3b237a8c.

* Revert "Don’t pod unless there are plugins (#9701)"

This reverts commit 732f79ee.

Remove checked in .lock, remove checked in cocoapods scripts in xcode project, let the automated test run pod install specifically for this test

Broken by 89af5ec8.

* Add cocoapods reason

* s/native/iOS