Stop building (unused) unlinked summaries for packages.

Improves update speed considerably (for `n` packages it saves us `n` needless calls to `pub get`).

This patch aligns the iteration patterns used by animations and
ChangeNotifier. They now both respect re-entrant removal of listeners
and coalesce duplication registrations. (Also, ChangeNotifier
notification is no longer N^2).

Fixes #7533

Previously, these classes where in material.dart, which meant they could
access private interfaces in that library. This patch moves them out
into their own files so that they need to play by the rules of the
public API.

Fixes #5969

It's not correct to set sizedByParent for
RenderCustomSingleChildLayoutBox because the delegate's size function
might depend on information other than the incoming constraints.

Previously the navigator wouldn't always call Route.dispose when it was
removed from the tree. After this patch, the navigator remembers popped
routes so that it can call dispose on them when it is removed from the
tree.

Also, improve some error messages around calling dispose() more than
once on routes and AnimationControllers.

Fixes #7457

The only client of this machinery was AnimationController.fling, but
it's easier for that function to just create the simulation it needs
directly.

Fixes #7216

I see these errors in Atom on my Mac. I'm not sure why they're not being
picked up by the bots.

Overflow handling works with clipping, adding an ellipsis on the last
line, or fading the last line.

Fixes https://github.com/flutter/flutter/issues/7271

It took me a while to figure out what was going on (I was removing a
listener after disposal). These asserts helped.

Our test script is getting complicated enough that doing your own
testing with a custom engine has become tedious. Now you can just do:

```bash
(cd ~/dev/flutter/; FLUTTER_TEST_ARGS=--local-engine=host_debug_unopt dev/bots/test.sh)
```

...to run all your tests (assuming your flutter repo is in
`~/dev/flutter` and your engine in `~/dev/engine`).

* MultiTapGestureRecognizer previously would assert if there was no
   competition.
 * GestureArenaTeam would always select the first recongizer as the
   winner even if a later recognizer actually accepted the pointer
   sequence.
 * debugPrintStack would fail a type check if maxFrames was non-null.
 * FractionalOffset.lerp would throw a null-pointer exception if its
   second argument was null.

Also, add a number of tests for previously untested lines of code.

This is handy for debugging a test. Communication is logged to:
* `flutter_driver_commands_{x}.log`, where {x} is an integer, and
* (if requested by user) to stdout

fixes #7473

* Update to Dart SDK `1.22.0-dev.6.0`.

* Update SDK summary generation to create spec and strong summaries.

* Updated to dev.8.0.

* Fixed console out.

Clarifying that Dividers aren't restricted to usage in lists and Drawers. Maybe no one else is confused about this but I didn't realize it until I found them used in the calculator demo (https://github.com/flutter/flutter/blob/8ca4caa4406046a683c0e2d2a5cf6118fa56fef7/examples/flutter_gallery/lib/demo/calculator/home.dart)

The demo of the SimpleDialog had some useful code that should really be part of
the framework. This patch extracts it into a SimpleDialogOption widget.

Remove debugCheckHasScaffold because it is unused.

Also, add tests for InkWell, SimpleDialog, and other widgets.

If the size is empty, then _updatePaintData will produce an invalid transform
that yields a NaN canvas bounds rectangle

Fixes https://github.com/flutter/flutter/issues/7431

That test intentionally has analysis errors to check how the tools react
to that situation.

Previously, the Slider used a drag gesture recognizer to move the head
of the slider, but when the slider was in a vertical scroller, the
recognizer would wait until the user moved the pointer by enough pixels
to disambiguate between sliding the slider and scrolling the scroller.

That worked fine for actual drags, but the slider should also move when
the user taps the track. This patch introduces a tap recognizer to
handle that behavior.

To avoid the slider's drag and tap recognizers from competing with each
other in the arena, this patch introduces the notion of a
GestureArenaTeam, which lets several recognizers combine to form one
entry in the arena.  If that entry wins, the team picks the first of its
recognizers as the winner, avoiding latency.

Fixes #7454

Now IconThemeData.fallback is a factory constructor and IconThemeData.of() does
the work of computing the fallback for its clients.

Also, add tests for ImageIcon and ListItems.

Previously, the ticker would not stop when it was muted because it thought it
was already not ticking.

With frameSync enabled, flutter_driver actions will only be performed
when there are no pending frames in the app under test. This helps with
reducing flakiness.

The underlying TextPainter is not exposed, so this patch exposes some
useful metrics that clients might want to read.

fixes #7433

* relax timeouts for some service protocol calls

* remove 'note that' text

Previously, it was possible for the test harness to bail
and the test runner to complete before the platform plugin
triggered the collection of coverage data. This fixes the
race condition such that the pending coverage collection
task is recorded immediately after starting the process.

* Add missing IJ metadata

* Updates

* Add modules metadata

This widget isn't tested and isn't used by Fuchsia or internally by Google. The
Hero widget is a better way of generating hero animations.

This patch adds tests for radio buttons, the date picker, as well as a
number of other classes.

We were checking similar things in two places. Now we check everything in one
place.

Also, fix a few minor bugs found by the test.

* Add example IntelliJ metadata (flutter-intellij#607).

Ensures example projects open cleanly out-of-the-box w/ the Flutter Plugin.

See: https://github.com/flutter/flutter-intellij/issues/607.

* Fixed IML files.