Drawer edge swipe convers entire screen

Refactor the Stocks app's settings

This will make it much easier to add more settings.

Fix crazy assertion.

Not sure what I was doing when I wrote this assertion, but I'm pretty
sure it's wrong. I'm guessing the change here is what I actually meant
to write.

Add more debugPaintSizeEnabled construction lines.

- padding is shown in blue with a darker blue around the child
- spacing (empty size boxes or padding) is shown in gray
- alignment from a RenderPositionedBox is shown with yellow arrows

When I tightened up the layout constraints for the Drawer in the
Scaffold, I ended up making the edge swipe detector cover the entire
screen.  This patch fixes that issue by putting the gesture detector for
the edge swipe just around the container with the proper width. We now
use a global key to maintain the state across hierarchy changes.

Material baseline grid

Proof of concept for Firebase support in Flutter framework

See https://www.google.com/design/spec/layout/metrics-keylines.html#

GridPaper updates

Fixed a tabs scrolling typo

Change how GridPaper works so that it's easier to plug in anywhere.
It now takes a child that it will paint the grid over.
It defaults to semi-transparent grid-paper-blue.
The line spacing is also more configurable now.

Optimize repainting in Scaffold

Fix tab fling scrolling when the last tab is selected

Previously, we triggered a layout (and hence a repaint) when sliding the
draw because we gave the draw loose constraints. The drawer uses an
Align to move itself to the proper side of the screen, so it can have
tight constraints, which makes it a layout boundary.

Also, don't trigger a layout just because the Scaffold rebuilds. There
isn't any state in the scaffold custom layout, so it doesn't need to
repaint just because we created a new instance of the delegate.

Finally, add the debugging infrastructure I used to find these issues.

generate docs for sprites

Reimplement TabBarSelectionState.of() using new methods

Tabs don't display items other than 0 and 1

The TabBarView wants to remap page indices during tab transitions, which
I broke when I refactored TabBarView.

Fixes #1119

Limit the size of the image cache

Fixed #1009

Handle trying to upgrade Flutter with no upstream

Move default back behavior to FlutterWidgetBinding

Fixes #1084

Remove BlockDirection in favor of ScrollDirection

Fix Scrollable.of()

`flutter start` crashes when port 8181 is in use

We'll probably renaming ScrollDirection to Axis in a future patch.

Fixes #151

Catch the error and log a warning.

Fixes #1050

TabBarView material gallery demo

Previously MaterialApp was responsible for ending the activity when the
back stack was empty. However, this behavior is more general than
material. This patch moves the behavior to FlutterWidgetBinding, which
has a global view of all the binding observers.

Fixes #1086

Make ancestorStateOfType() and ancestorRenderObjectOfType() support
subclassing.

Fixes https://github.com/flutter/flutter/issues/1087