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

* show device list in flutter doctor output
fixes https://github.com/flutter/flutter/issues/5625

Fixes https://github.com/flutter/flutter/issues/5234

The iOS transition is the more buggy part of this feature, and it wasn't
disabled. Let's just leave them enabled while I work on improvements.

* improve device matching error message
fixes https://github.com/flutter/flutter/issues/5675

One of the drawer items was dsiabled but still clickable which
led to inconsistent icon coloring. THis commit makes this item
actionable. Fixes #5683.

Subheading title was too close to the actual example. This commit
increases the size of its box. Fixes #5682.

The floating action button inside of the Pesto demo now opens up
a snackbar. Fixes #5685.

BUG=https://github.com/flutter/flutter/issues/5599

Implement flutter format, fixes https://github.com/flutter/flutter/issues/5338

Added a widget that cross fades two children while animating the
size of the parent based on the children's interpolated sizes.

Fixes https://github.com/flutter/flutter/issues/5592

See https://github.com/flutter/flutter/issues/5570

Also added a regression test for the back gesture on iOS and android.

* fix getDeviceById to match exact name
fixes https://github.com/flutter/flutter/issues/5508

* peg dartdoc to a specific version

* add some documentation

* apply the fix to dev/bots/docs instead

Previously, it was unclear that the middle slider was disabled.

Fixes #5517

Fixes https://github.com/flutter/flutter/issues/5283

Other changes in this patch:

Rename OffStage to Offstage.
Fixes https://github.com/flutter/flutter/issues/5378

Add a lot of docs.

Some minor punctuation and whitespace fixes.

1: If a route is already dismissed when it's popped, there's no point
trying to animate heroes, because it's going to be gone before the
heroes code can look at it.

2: If a hero animation finishes just as a new one is starting, we
previously blew away the state for the starting one. Now we correctly
segregate the "starting up quest" variables from the "actively ongoing
quest" variables.