Refactor service-related code to be shared between android and IOS.

Improve asserts around BoxConstraints

The IOS code is totally untested. Need a Mac to test it.

Negative constraints never make sense, so catch those too.

Make RenderObject.layout's isNormalized assert use the newer more fancy
debug version of isNormalized.

Upgrade command shouldn’t validate project, fixes #1745

Teach PageableList about scroll anchors

Teach ScrollableList about scroll anchors

fix an issue with logging ios simulator output

Introduce globals

Tapping through drag targets.

Factor out the HitTestBehavior logic so that RenderMetaData can use it.

Use that in DragTarget.

ignore derived resources in ios/build

Add a refresh command that rebuilds the snapshot and reloads it on th…

Add scroll anchor for Block

This patch teaches block how to anchor its scrolling to the end rather than the
start.

Fixes #136

Draggable: childWhenDragging, maxSimultaneousDrags

Fixes issue with replacing the root node

filter offline devices from notifications

rename the service protocol extensions

This provides a fast way to iterate on changes to a Flutter app that only
involve updates to Dart code and do not require a full build and install
of the FLX and APK

Remove FLUTTER_DEV environment var

This check is triggering even for folks who don't have FLUTTER_DEV set, which
is breaking their toolchain because we're not running `pub get` on the
flutter_tools package.

Update docs for benchmarks.

removed kStatusBarHeight constant

Preliminaries for scroll anchoring

These classes now share more code and have feature parity.

Gallery Demos: button, dialog, snack bar

Added button, dialog, and snack bar gallery demos.

Split gallery main.dart into files in the lib/gallery subdirectory.

Enable TabBarSelectionState to deal with the PageStorage saved selected value no longer equalling any value.

Changed the color of Dialog text to match the theme's caption color.

Also: uppercased tab labels per #1617

Fix drawer in accessibility mode