To avoid orphaning people on the deprecated alpha branch, this patch teaches
`flutter upgrade` to switch to the master branch.

This commit renames all debugAssertValid methods to
debugAssertIsValid and assert BoxConstaints validity in
constructors. Fixes #5807.

BUG=https://github.com/flutter/flutter/issues/5373

This allows us to simplify the logic around inherited widgets e.g. in
the Image widget.

Changed the text styling to make use of the current theme so that
it doesn't break when the user selects the dark theme.

* turn verbs into nouns for gallery homepage

* shorter is better

In that they never create a window with an OpenGL context and the works.

... in place of manual process wrangling.

I forgot that it was possible for the root view to get marked dirty
without getting a new widget. This fixes that case to work.

I did a pass through some of the code cleaning minor things up.

Fixes https://github.com/flutter/flutter/issues/5776

Fixes flutter drive breakage introduced in d2fda677.

The drawer was confusing without adding much value. It was
especially confusing when wanting to go back to the Gallery on iOS.
Fixes #5713.

This adds and enables a raft of new analysis options for the flutter repository, many of which are commented out until we clean up our code and/or address any linter false positives.

This aligns the comments and fixes some misspellings in the three related analysis options files.
There will be a follow on PR with more controversial changes to the repo level analysis options.

update the analysis options used by flutter analyze when analyzing source outside of the flutter repo.

When flutter run is used on a Mac and no devices are specified or attached, suggest launching a simulator first. Fixes https://github.com/flutter/flutter/issues/5674

Previously, pumpWidget() would do a partial pump (it didn't trigger
Ticker callbacks or post-frame callbacks), and pump() would do a full
pump. This patch brings them closer together. It also makes runApp run a
full actual frame, rather than skipping the transient callback part of
the frame logic. Having "half-frames" in the system was confusing and
could lead to bugs where code expecting to run before the next layout
pass didn't because a "half-frame" ran first.

Also, make Tickers start ticking in the frame that they were started in,
if they were started during a frame. This means we no longer spin a
frame for t=0, we jump straight to the first actual frame.

Other changes in this patch:

* rename WidgetsBinding._runApp to WidgetsBinding.attachRootWidget, so
  that tests can use it to more accurately mock out runApp.

* allow loadStructuredData to return synchronously.

* make handleBeginFrame handle not being given a time stamp.

* make DataPipeImageProvider.loadAsync protected (rather than private),
  and document it. There wasn't really a reason for it to be private.

* fix ImageConfiguration.toString.

* introduce debugPrintBuildScope and debugPrintScheduleBuildForStacks,
  which can help debug problems with widgets getting marked as dirty but
  not cleaned.

* make debugPrintRebuildDirtyWidgets say "Building" the first time and
  "Rebuilding" the second, to make it clearer when a widget is first
  created. This makes debugging widget lifecycle issues much easier.

* make debugDumpApp more resilient.

* debugPrintStack now takes a label that is printed before the stack.

* improve the banner shown for debugPrintBeginFrameBanner.

* various and sundry documentation fixes

BUG=https://github.com/flutter/flutter/issues/5351

* Udpate to Dart `1.20.0-dev.1.0`.

Udpate to Dart `1.20.0-dev.1.0` and corresponding `analyzer` package.

* Added `--no-packages-dir`.

* Revert extension to master.

* Added ignores.

* Review nits.

* More nits.

This issue got fixed by a recent check-in, but I had a test specifically
for this incarnation so we should probably keep it just in case.

Closes https://github.com/flutter/flutter/issues/5630

Update engine revision to pull in fixes for crashes on arm64 due to missing CRC32 instruction. (#5774)

This updates the flutter analyze command to use the .analysis_options_flutter_analyze in the repo root when either the --flutter-repo flag is supplied or the sources being analyzed reside in the flutter repo.

Previously, if a StatefulWidget was marked dirty, then removed from the
build, then reinserted using the exact same widget under a widget under
a LayoutBuilder, it wouldn't rebuild.

This fixes that.

It also introduces an assert that's supposed to catch SizeObserver-like
behaviour. Rather than make this patch even bigger, I papered over two
pre-existing bugs which this assert uncovered (and fixed the other
problems it found):

   https://github.com/flutter/flutter/issues/5751
   https://github.com/flutter/flutter/issues/5749

We should fix those before 1.0 though.

In the interest of using the name in the case of Material steppers,
this commit renames Step curve to Threshold.

This eliminates all the issues around the horizontal page transition. I also improved the back gesture animation, and added fling support.

BUG=https://github.com/flutter/flutter/issues/5678
BUG=https://github.com/flutter/flutter/issues/5622

Related: b5f763b4

Fixed a bug where the size of the AnimatedCrossFade would always
start from the size of the first child, irrespective of the
initial crossFadeState argument.

Closes #5702

Update transitions_perf_test.dart

Update simple_smoke_test.dart

Fixes #5393.

* adjust channel_test to be less specific
fixes https://github.com/flutter/flutter/issues/5716