Execute rename fixit

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #2233

Fixes #1482

Fixes #1382

Fixes #1278

Fixes #774

Fixes #581

Fixes #459

Also, change the keys to be explicitly pointer ids.

Fixes #202

add an atom launch config to the starter app

fix a regression in adb forward

fix a launch issue when the user has deleted the app

Enable always_specify_types lint

And fix the zillion issues that uncovered.

Revert "Merge pull request #2639 from Hixie/always_specify_types"

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

Almost enable always_specify_types lint

Enable strong mode again.

And fix the zillion issues that uncovered.

Handle the case of reparenting while updating children

Instead of trying to flush the detached children from the child list, we keep
the set of detached children up to date and query on every read.

show the error codes in flutter analyze --watch

flutter analyze test

AspectRatio should attempt to fit its height

Migrate flutter analyze config to options.

If there's not enough height for the given aspect ratio, we now try to see if
using the height to infer the width will fit the given constraints. The
algorithm we use is similar to the one we use for RenderImage.

Fixes #2620

Update engine

More groundwork to get `analyze` and IDE output to agree.

See: https://github.com/dart-lang/sdk/issues/25723

Test that flutter analyze catches no error if two imported libraries
have the same name.

Also, make tests know how to find the flutter root and fix style in one
test to be consistent with the rest of the file.

Analyze command cleanup.

Run "pub get" if needed in the flutter build command