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

This patch finishes documenting all the symbols except for those related to
scrolling.

* Add a text formatter interface used by EditingText. Provide some default implementations.

* self nits

* Handle -1 selection offsets

* review notes

* simplify regular expression

* Add whitelisting formatters. Use a custom phone number formatter in text demo.

* review notes

* not being able to addAll(null) is pretty annoying

* review notes

* partial tests

* Add tests

* didn’t end up needing mockito

* move to services

Creates another Decoration for drawing outside the decorated box with a gradient to emulate the shadow.

Lets the cupertino transition page's background be transparent.

Fixes #9321

...because it clearly is.

* Implement

* Don’t scale the fractional offsets since it’s easier to use

* review notes

* fix nit

FlutterCommand.runCommand subclasses can optionally return a FlutterCommandResult which is used to append additional analytics. 

Fix flutter run timing report and add a bunch of dimensional data

backgroundColor -> color
backgroundImage -> image
BackgroundImage -> DecorationImage

If the user specified a non-exact device id, it was producing
an exception whereby we were trying to listen to the
`getAllConnectedDevies()` stream twice.

A NestedScrollView lets you implement patterns where you have a header, tabs,
and additional scrollers inside the tabs.

Fixes #8359

Previously, ScrollPosition did not know about ScrollActivities. However, all
the concrete subclasses of ScrollPosition that we know about need to use
ScrollActivities, so they ended up with a bunch of delegate boilerplate code.

This patch teaches ScrollPosition about ScrollActivities but doesn't have any
opinion about how to start or interact with those activities.

This patch is more refactoring to prepare for nested and linked scrolling.

It causes the test to be flaky, see https://github.com/flutter/flutter/issues/8986.