More elaborate RenderBox example

Reimplement the theme transition animation by actually animating the Theme

As part of this:
 - A lot of classes got new lerp functions, including e.g. TextStyle.
 - Theme's constructor story got overhauled. You can now configure
   everything if you really want to, and we're better about defaults.
 - Material no longer automatically animates its background color.
   (It still does for its shadow.)
 - Tabs try to get the indicator color from the theme.
 - The fields in ThemeData got reordered for sanity.
 - Theme.== and Theme.hashCode got fixed.
 - Typography got a bit of a spring cleaning.

Fixes #613.

Skip "list of devices" header from adb

Sometimes "adb devices" prints a header. We should skip over the header
instead of complaining that we don't recognize it.

Fixes #1293

Rename ViewConstraints to ViewConfiguration

Rename _Child to _ScaffoldSlot for clarity.

Make 'flutter analyze' support analyzing arbitrary files

Activity clean-up

Also, some trivial fixes for things that I found while playing with
the rendering library directly.

Include BoxDecoration description in Container toString

Prepare flutter analyze for dart 1.14

And rootConstraints to configuration.

This type and its variable have nothing to do with Constraints.

Fixes https://github.com/flutter/flutter/issues/829

Before we didn't know how to find the packages of random files. Now we do.

Turns out Android crashes if the colour is not opaque, so we enforce
that at the Dart level.

Also, since label and colour are both actually optional, make them
named arguments.

fix framework to match new mojo sdk

The dart bindings changed semantics in a non-compatible way.

Remove Firebase flutter packge

fix links to new website

Update progress_indicator widget example

Update the progress_indicator demo: it was using Title explicitly, which is no longer needed.

Defend against a null color in updateTaskDescription. The color field in the TaskDescription struct (activity.mojom) isn't nullable.

Fixes #1248

Have BoxDecoration default to one-line dumps

Style nits in a rendering example

Tooltips

Introduces a new Tooltip class.
Adds support for tooltips to IconButton and Scaffold.
Adds some tooltips to various demos.

Also some tweaks to stack.dart that I made before I decided not to go
down a "CustomPositioned" route.

Stocks has both tabs reified in the wiget tree

PageStorage storage identifier should include the context widget's key

We were recomputing which widgets to show only when we were on the other side
of the repaint boundaries. That doesn't work well for pageable lists because we
come to rest exactly on a repaint boundary, which means we don't cull the other
page.

After this patch, we recompute the set of widgets using an edge-trigger when we
hit the boundary. That's better than using a level-trigger so that we don't
continuously recompute the set of widget as we sit at the boundary.

Switch back to GitHub hosting of stock data

The Firebase server seems to have changed behavior and is not giving us a List
instead of a Map. This patch switches us back to GitHub, which just serves the
same flat files all the time.

Remove flutter_sprites sound_manager.dart

Tweaks near Material, BoxDecoration, implicit animations.

Some more asserts and toString info.
Reorder some code to group lerp-related functions.

clarify that start defaults to checked