Scrollable's callbacks should follow a state machine

remove the isConnected() method from device

Now onScroll callbacks are always bracketed by onScrollStart and onScrollEnd
callbacks.

Fixes #1822

Add tooltips to FloatingActionButtons

SizeObserver crusade: Remove EnterExitTransition

Remove some prints in tests.

Add CheckedPopupMenuitem, update the Stocks demo

Fixes #1875

Simplify demo template

We don't need these keys. Also, improve style in several places.

Fixes #2225

...and friends.

some performance optimizations for starting apps

Handle conflicting 'library' identifiers

Move update_packages.dart to `flutter update-packages`

Update engine revision to pick up the fixes for instability on iOS

Also, handle the new directory structure of the flutter repo.

add timing info for flx creation

SizeObserver crusade: RawInputLine

decouple `flutter drive` from `flutter start`; make things in `flutter_tools` more testable

flutter start's method of finding devices to run the app on is not suitable for flutter drive.

This commit also refactors several tool services to allow mocking in unit tests.

Pin analyzer package so that we're consistent

Gallery Menu Demo etc

Now that we don't require the Dart SDK to be in your path, it's hard to run
./dev/update_packages.dart. Instead, you can now run `flutter update-packages`.

Fixes #1906

See the comment in the patch for details.

SizeObserver crusade: Dismissable

Update engine revision

Remove examples/fitness

We originally wrote examples/fitness to be an app which all
members of the Flutter team could carry on their phones and
use every day.  It served us well for testing of Text input,
Keyboards and writing/reading JSON.  It's never actually become
a real carry app, so lets just let it go for now.

@abarth @collinjackson

Ignore `flutter analyze` errors via analysis options.