With this change you can now create "wrapping" text fields that do not show the new line button:

```dart
new TextField(
  maxLines: null,
  keyboardType: TextInputType.text,
);
```

In the event that no Dart VM's exist or are connectable, will instead
await for a new Dart VM to show up. Will no longer return null when
calling `getMainIsolatesByPattern`, instead returning either a list of
isolates or timing out.

Reason for revert: The package:flutter_gallery_assets has removed some images which are required for the examples/flutter_gallery, so the gallery build is failing (only discovered after landing, since gallery doesn't seem to get built during github PR presubmit checks)

This CL

  * rolls `engine.version` to flutter/engine@b148e628 (which includes dart sdk 2.1.0-dev)
  * rolls `goldens.version` to flutter/goldens@6c45fafdf (which includes updates due to skia changes in engine)
  * changes `platform.dill` to `platform_strong.dill` in various places due to flutter/engine@a84b210b
  * adds explicit `environment: sdk: ">=2.0.0-dev.68 < 3.0.0"` constraints to `pubspec.yaml` and `pubspec.yaml.tmpl` files (since pub defaults to `<2.0.0` if omitted) 
  * upgrades to newer versions of various 3rd party packages (to ensure transitive dependencies have `<3.0.0` sdk constraint)

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

In certain cases, the test would fail before creating the (lazily created) compiler object, and then we'd
try to call shutdown() on null in those cases.

Fixes #18610

Allows the cupertino picker to be scroll infinitely by adding builder.

This adds the animation links for illustrations of the Transition widgets, as well as adding a cross-references to the other transition widgets in the "See also" for each of their docs.

See https://github.com/flutter/flutter/issues/19434

This changes the flutter tool to just try 10 times before giving up when running "flutter upgrade". Infinite retries can hang bots, and really don't provide a lot of help: if we've failed to upgrade for for nearly a minute, trying every five seconds, then something is just not responding.

Also, changed the bot default warning level to "normal" from "all", because the solver messages are VERY verbose: several megs of output for doing packages get on Flutter. "normal" will give warnings, user messages and errors, which should be sufficient to diagnose problems on the bots without spamming the log.

I removed the retrying for building the snapshot on flutter.bat because we don't do that on the other platforms, and because I can't imagine how running it again would give a different answer.

I also fixed a problem in the whitespace detection when no files matched the type of file that it is looking for, and removed the code that waits until failure to print the logs on setup, since reducing the log output made a huge difference.

This reverts commit 05c2880a.

Auto-roller completed checks. Merging.

Adding CupertinoActionSheet, showCupertinoModalPopup

* Visibility widget

This attempts to address the confusion around how to hide a widget subtree.

* Apply review comments

* More clarifications

This includes the following changes :

e54bc4ea1 Fixed invalid call site of runWithEntrypointAndCallback (#5984)
764884b91 Removed callback for HeadlessDartRunner (#5983)
91537abba Revert "Temporarily add travis/analyze.sh back for Chrome bot (#5961)" (#5966)
3501acb70 Roll src/third_party/skia 9c9611fcc1bb..0d5d0659a684 (7 commits) (#5980)

Somehow I forgot to say "super.tap()" when calling "tap()" on the new
superclass, so it was just recursing infinitely but ended up actually
crashing on the first reuse of the finder.

The error was previously swallowed, I made this print it instead.

This fixes https://github.com/flutter/flutter/issues/18057

Add minOverscrollLength to make CupertinoScrollbar thumb correct size in long scroll views.