* Run flutter tests in preview-dart-2 mode on travis flutter builds.

* Run dart2 tests on osx. Run dart tests in dart2.

* Fix name camelCase

* Default options to empty array, rather than null

* Troubleshoot failures

* More logging

* Troubleshoot: run single test

* Troubleshoot: run 15 tests

* Troubleshoot: run 15 tests with fix

* Try limit concurrency to 1

* Limit concurrency for preview-dart-2 tests to 4

* Move dart2 tests to allow_failures section

* Reinstate tests_dart_2 shard

* Raise concurrency to 8

* Reuse compiler across multiple test runs

* Allow to switch entry points when recompiling.

Actually use single compiler to incrementally recompile all tests executed by 'flutter test'.

* Remove leftover commented code

* Fix comment

* Lints

Changes since the last roll:
  - Specify sdkSummary when compiling via frontend server (#4733).
  - Fix traversal order for a11y scrolling (#4726)

accidentally missed due to named parameters being omitted.

Adds more actionable error messages for users of the most common Linux
distributions. We could improve this by checking the current
distribution and emitting only the appropriate error message. We could
further improve that by only emitting the install instructions if we
determine the appropriate package is not installed.

See: https://github.com/flutter/flutter/issues/6207

I found that some ValueListeners want to know when they should start
doing work (e.g. if the value comes from polling a network resource).

This roll contains:
* Make deprecated API unavailable (https://github.com/flutter/engine/pull/4722)
* Remove unavailable API in FlutterDartProject.h (https://github.com/flutter/engine/pull/4723)
* remove unavailabe API from FlutterDartProject.mm (https://github.com/flutter/engine/pull/4724)
* Prepare to enable global type flow analysis in AOT (https://github.com/flutter/engine/pull/4725)

* Add more haptic feedback varieties

* tests

* un-meta-ify the test

Fixes https://github.com/flutter/flutter/issues/15002

This is to fix #14931.

* If example code is not found, render a message instead of an endless spinner
* Trim codeTags to avoid lookup issues with windows carriage returns
* Trim \r on Windows off the end of code blocks so they're consistently \n
* Add a test to ensure sample code parses if built on Windows
* Add a comment about why we trimRight()

Fixes #14820.

* Revert "Revert "Add android license verification to doctor and some refactoring" (#14727)"

This reverts commit d2602947.

* Add tests, fix sdkManagerEnv and use it consistently, and rearrange Status object model

* AnsiSpinner needs to leave the cursor where it found it.

* fix tests

* Const constructor warning only shows up on windows...?

* Avoid crash if we can't find the home directory

* Make pathVarSeparator return a string in the mock

* Implement review comments

* Fix out-of-order problem on stop

Fixes https://github.com/flutter/flutter/issues/14975

* roll engine version in flutter/flutter to b05efc204090f430387398d3c35589571a2fe16b

* Fix analyzer warnings.

The downcast was crashing when toggling hasNotch for BottomAppBar.

Dart is migrating to .dart_tool/ as the location for cached artifacts
and other temporary files generated by tooling in the SDK. As part of
this, pub will be migrating from .pub to .dart_tool/pub.

In future, this path will also be used for other tooling, such as package:build.

We can't use .tar.xz on Mac because although it can unpack them on the command line (with tar), the "Archive Utility" that runs when you double-click on them just does some crazy behavior (it
converts it to a compressed cpio archive, and when you double-click on that, it converts it back to .tar.xz, without ever unpacking it!)

So, this changes the script to use .zip for Mac, and the files are about 220MB larger than they need to be. 

* Revert "Disable a text field test that fails on some Macs with libtxt (#14895)"

This reverts commit aa04a056.

* Revert "Roll engine to 33b88173f3820690169348859bbdc29133179e0b (#14832)"

This reverts commit 44592238.

* Revert non-engine reverts

https://github.com/flutter/flutter/issues/14893

* Doc improvements for animations

libtxt is now the default text renderer

* update the IntelliJ metedata templates

* fix test expectation

* Add --preview-dart-2 to 'flutter drive'

* Run driver side in --preview-dart-2 mode.

* Fix test

The Floating Action Button adds some margin around it for the notch.
So we need to compute a notch even when the FAB and the Bottom App Bar
doe not overlap.

30+4 has made some changes to the remoting protocol that are incompatbile
with a test harness running 30+3 (e.g. adding a type='initial' field to the
first message)

* Fix snapshot fingerprinting in --preview-dart-2 mode.

This is a follow up to PR #14775 - instead of treating dill file
as an input treat as intermediate file and don't fingerprint it.

Make sure to always use original main Dart file as an entry
point for fingerprint calculation.

This fixes an issue that AOT snapshot would not be recompiled in
the preview-dart-2 mode if entry point changes, e.g.

$ flutter build aot -t t/x.dart --preview-dart-2
$ flutter build aot -t t/y.dart --preview-dart-2

The second invocation would not build AOT snapshot.

(This issue is visible on the microbencmarks bot)