Fixes https://github.com/flutter/flutter/issues/11539

* Bump Dart SDK to 1.25.0-dev.9.0

* add link to sdk bug

* Make tear-offs cachable for RenderSemanticsGestureHandler

Fixes https://github.com/flutter/flutter/issues/11552

* comment fix

* refactor

* a11y: handle left/right scrolls correctly

* fix keep alive test

* fix scaffold test

Don't trigger an assert when markNeedsSemanticsUpdate is called multiple times in edge cases (#11544)

* Don't trigger assert if a render object ceases to be a semantic boundary

This bug was exposed by https://github.com/flutter/flutter/pull/11309, which caused the following assertion to trigger when scrolling in the Animation demo:

```
The following assertion was thrown during _updateSemantics():
'package:flutter/src/rendering/object.dart': Failed assertion: line 2626 pos 16: 'fragment is
_InterestingSemanticsFragment': is not true.
```

A minimal reproduction of the bug can be found in `semantics_10_test.dart`, which has been added as a regression test for the bug by this PR.

Looking at that test, here is a description of the faulty behaviour:
1. During the second `pumpWidget` call `RenderExcludeSemantics` marks itself as needing a semantics update (due to excluding going from `false` -> `true`).
2. This causes the nearest ancestor with semantics information (here: `RenderSemanticsAnnotations` representing the "container" Semantics widget) to be added to the `_nodesNeedingSemantics` list.
3. `RenderSliverList` (implementation behind ListView) marks itself as needing a semantics update (due to its changing children).
4. This causes the `RenderSemanticsGestureHandler` to be added to the `_nodesNeedingSemantics` list.
5. Next, canDrag is updated from `true` -> `false`. This means, `RenderSemanticsGestureHandler` is no longer a semantics boundary, it marks itself as needing a semantics update.
6. The nearest ancestor with semantics (`RenderSemanticsAnnotations`, the "container") is added to the `_nodesNeedingSemantics` list (this is a no-op because it is already in the list).
7. During `flushSemantics`, the `_nodesNeedingSemantics` list is walked. The first entry (`RenderSemanticsAnnotations`) updates the semantics tree to only contain the container widget and drop everything else (= no children of the ExcludeSemantics widget are walked).
8. The second entry (`RenderSemanticsGestureHandler`) is updated. It does not add any semantics of its own and is no longer a semantics boundary. Therefore, it wants to merge its descendent semantics into its parents. Here is where the assert throws because the algorithm assumes that every entry in the `_nodesNeedingSemantics` list will produce and own an `_InterestingSemanticsFragment` (passing your semantics on to your parents is not interesting).

The problem here seems to be step 4 in combination with step 5. In step 4 we rely on the fact that `RenderSemanticsGestureHandler` is an (explicit or implicit) semantics boundary and that it will be able to absorb the semantics change of `RenderSliverList`. This is true
at this time. However, in step 4 `RenderSemanticsGestureHandler` decides to no longer be an (explicit or implicit) semantics boundary and our assumption from step 5 becomes incorrect. We did nothing to correct this assumption.

This PR removes a node, that could potentially cease to be a (explicit or implicit) semantics boundary from the `_nodesNeedingSemantics` list to fix that problem. Please node that this does not mean that the node's semantics will not be updated: The node's closest ances
tor with semantics is added to that list during the `markNeedsSemanticsUpdate` call. During `flushSemantics` we will walk from this node to update the semantics of it's children (if changed), which will include the node in question.

* tiny fix

* simplify test

* analyzer fixes

* review comments

This change re-introduces skipping snapshot builds if input sources (and
outputs) have not changed since the last snapshot build, with a bugfix
to include the entry-point source in the checksum used to check whether
rebuild can be skipped. This ensures that the following sequence
invalidates the cached build, resulting in two snapshot builds:

  flutter build ios lib/foo.dart
  flutter build ios lib/bar.dart

This reverts commit 3d5afb5a.

* Allow tapping on TabBar indicator to switch tabs

* fix semantics

* review comments

Roll engine in order to fix regression of AOT snapshot build time.

I forgot to do this when I updated our test package.

The most recent Flutter IntelliJ plugin replaces FLUTTER_MODULE with
WEB_MODULE and eliminates the exclusion of packages/ directories.
Use of the packages/ directory was turned off by default months ago, and
is replaced by the .packages file.

* Adds more customization options to the Chip widget

Includes:
- Custom Tooltip message for the delete button;
- Custom background color for the chip
- Custom delete icon color
- Custom label text style

* Adds missing type annotations to tests and improves documentation.

* Tweaks labelStyle field documentation

Also, add tests to verify that our coverage is actually being tested!

* Adding tests for animationStatus

* remove comments

* animateTo is allways forward

* clearify docs

* review comments

It was previously possible for event dispatch to occurr during the
brief window where the tree had been marked dirty but before it had
been relaid out by reassemble, which would cause assertions to fire if
someone did a hot reload while touching the device.

* Do not schedule animation if already at the target value

* Partially fixes https://github.com/flutter/flutter/issues/11495.
* Also includes a fix for Cupertino button to always run the tap animation even if the finger is immediately lifted from the screen (uncovered by a test failure).

* refactorings

* more tests

* test clearifications

* remove Listener

* fix lints

* fix async issue

In a Travis environment, the test package is exiting the process after
completing the tests.
See dart-lang/test@d1057c4

The flutter test command calls the test package's main() and then expects to
do other work afterward.  The exit prevents flutter test from writing the
new coverage results, causing the coveralls tool to run against an old
lcov.info file.

This reverts commit 0cfd3dec239faf3c13ce759df15ddab226545e8c.

Do not throw if a hot reload is attempted when all Flutter instances on the device have been stopped (#11504)

This can happen if an Android host app has been paused but its process is still running

Add Diagnosticable base class and documentation

* FadeInImage: shows a placeholder while loading then fades in

* fix dartdoc quotes

* license headers; imports

* use ImageProvider; docs; constructors

* _resolveImage when placeholder changes

* address comments

* docs re ImageProvider changes; unsubscribe from placeholder

* rebase

* address comments

* refactor commands_test to choose a free port for the service protocol

* discover the service protocol port

* add a todo

* Revert "Support space- and backslash-escaped dependencies (#11090)"

This reverts commit e6bafd0b.

* Revert "Skip AOT snapshot build if inputs are unchanged (#11084)"

This reverts commit b5e522e2.

* perform the initial poll for devices quicker

* add a Poller class

* test the new Poller class