Previously the floating action button would disappear during transitions. Now
we animate properly. I've also centralized the animation in Scaffold instead of
spreading it across the Scaffold and the FloatingActionButton.

Fixes #1718

This introduces the key parts of a paginated data table, not including
the built-in pagination features.

* Provide more data for the data table demo, so there's data to page.

* Introduce a ChangeNotifier class which abstracts out
  addListener/removeListener/notifyListeners. We might be able to use
  this to simplify existing classes as well, though this patch doesn't
  do that.

* Introduce DataTableSource, a delegate for getting data for data
  tables. This will also be used by ScrollingDataTable in due course.

* Introduce PaginatedDataTable, a widget that wraps DataTable and only
  shows N rows at a time, fed by a DataTableSource.

...and fix some grid and table intrinsic issues it uncovered.

* fix a race condition with isolate notification

* return a future

* Fix fallout from intrinsics changes

* Move away from isInfinite in favor of isFinite

This patch updates how we generate xcconfig files to match what
xcode_backend.sh expects.

This reverts commit 215e1b89.

It broke the Mac build: https://build.chromium.org/p/client.flutter/builders/Mac/builds/1097

There are many more places we can use this annotation. This patch starts out
small to test the waters.

This patch starts using the mustCallSuper annotation for several of the key
lifecycle callbacks in the framework. I haven't added it to didUpdateConfig
because there are a large number of non-compliant overrides. We should discuss
whether we want to use it there.

As requested by the material design team.

Fixes #4182

Currently this service just returns mock data, but it exercises the plumbing.

Update analyzer dep to 0.27.4-alpha.9

Update analyzer dep to 0.27.4-alpha.9 to enjoy analyzer perf improvements (https://codereview.chromium.org/2011183004/) (and keep in sync with the SDK).

(This is a revisit to https://github.com/flutter/flutter/pull/4253.)

I pulled the trigger to land the previous patch too quickly and missed a
number of comments.

We used to use this mechanism to paint scrollbars, but it's awkward. The
new approach to scrollbars is much cleaner. This mechanism has no other
clients, so we should remove it.

* show build progress; print app sizes

* add todo

* review comments

* remove unused import

This example shows how to build a basic app using a custom Xcode project.
Future patches will bring the functionality up to par with hello_android.

The new mojom.dart code makes mocking services a bit tricky. I've filed
https://github.com/domokit/mojo/issues/786 about improving that.

* run pub get (w/ symlinks) for flutter drive

* review comments

Instead of embedding Flutter.framework and BuildFlutterApp in the Xcode
project, we store these in flutter.git, where we can reference them.

We'll use this functionality to implement some subtle behaviors for tooltips.

* modernize `flutter drive` w.r.t. debug/profil/release options

* make error message prettier

There are still many more left before rendering.dart is complete.