* Adds `empty_statements` (new in `0.1.21`).
* (Re)enables `iterable_contains_unrelated_type` (fixed in linter#245).

This slipped in with an earlier commit.

- show the next error fully after a hot reload
- hide _AssertionError in stacks
- immediately rebuild after a reassemble, so that hit tests work
- catch errors when notifying global key listeners

This was a minor typo in the original code. It makes the license display
slightly cleaner.

Previously we would rebuild every route on the second animation frame to
rejigger the offstage bit and the animations. Now we build the page once and
update the offstage bit in place and update the animations using
ProxyAnimations.

DevFS asset support and deletion support

Update Dart (1.19.0-dev.0.0) and analyzer (0.27.4-alpha.19).

Also, add a few more debugging flags.

Fundamentally the core problem was that we were not saying how wide a
date picker should be. It should be 330 pixels, if I'm measuring the
spec's mocks correctly.

Fixes https://github.com/flutter/flutter/issues/4910

This patch adapts the AppBar to feel more like iOS by centering the title.

Fixes #4962

We should center the title of flexible space bars on iOS.

Related to #4962

* This reverts commit 5e7e7b6e.

* default to lib/main.dart

BUG=https://github.com/flutter/flutter/issues/4904

This reverts commit 32ad81c8.

We'll use this field to adapt material widgets to iOS.