Eliminates hardcoding of Typography.white in favour of picking up the
platform default typography from ThemeData.

Previously, we were getting double padding: both inside and outside the button.
This patch moves all the padding inside the button so that the whole region is
hittable and the text is positioned correctly.

Fixes #6059

This requires all AnimationController objects to be given a
TickerProvider, a class that can create the Ticker.

It also provides some nice mixins for people who want to have their
State provide a TickerProvider. And a schedulerTickerProvider for those
cases where you just want to see your battery burn.

Also, we now enforce destruction order for elements.

In the interest of using the name in the case of Material steppers,
this commit renames Step curve to Threshold.

We now use the `@required` annotation to encourage developers to
explicitly set onPressed and onChanged callbacks to null when that would
disable the widget.

Fixes #287

Fixes 3544

For consistency.

Fixes #4142

This reverts commit 55f9145e.

Turns out that this commit breaks apps that use the material library,
because of the _errorTextStyle DefaultTextStyle which has inherit:true.
Just setting it to false doesn't work, unfortunately, because then you
hit some sort of issue with merging that text style with others that
have inherit:true.

To make it clear that this constructor requires an explicit style. Also
throw a descriptive error recommending the inherit constructor for
styles with the inherit bit set.

Fixes #3842

Making progress towards document all public APIs in material.dart. We're still
missing a few odds and ends (as well as missing docs in tabs.dart,
tooltip.dart, and two_level_list.dart).

This patch completes the circuit on this library. The next step is to go
through and add docs to anything we missed.

Instead of incorporating the margin into the button, introduce a ButtonBar
widget that supplies the proper spacing between the buttons. Also, make these
buttons more configurable via ButtonTheme so that dialogs can change the
minWidth and padding of the buttons as required by the spec.

Fixes #1843
Fixes #3184

A flow layout is optimized for reposition children with transformation
matrices. A flow layout can animate the position of its children very
efficiently.

They should automagically disable after the first tap.

Previously, the Dismissable widget was animating down to zero width off
screen. Now, we tell it to skip the resize animation.

Fixes #3030

Fixes #617

Fixes #463

Adds some names for common FractionalOffset values.

* justifyContent -> mainAxisAlignment
* alignItems -> crossAxisAlignment
* FlexJustifyContent -> MainAxisAlignment
* FlexAlignItems -> CrossAxisAlignment

Fixes #231

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #1382

Fixes #1278

These files are already in the "material" folder. They don't need to be
prefixed with material again.

Fixes #702

The example in the spec with multiple actions is an anti-example.

Fixes #1876

Fixes https://github.com/flutter/flutter/issues/1331

Hopefully this will be enough to start with. If this continues to be a
point of confusion we can see about adding more documentation or
changing the API somehow.

Each layer is supposed to reexport the parts of the previous layer
that are part of its API.

- In painting.dart, export from dart:ui all the Canvas-related APIs
  that make sense to be used at higher levels, e.g. PaintingStyle.

- Delete painting/shadows.dart. It was dead code.

- In rendering/object.dart, export all of painting.dart.

- In widgets/basic.dart, export all of painting.dart and
  animation.dart. Some classes in animation/ are renamed to make this
  less disruptive and confusing to the namespace.

- Split out Stocks back into an import model rather than a part model,
  so that it's easier to manage its dependencies on a per-file basis.

- Move Ticker to scheduler library.

- Remove as many redundant imports as possible now.

- Some minor nit picking cleanup in various files.

This patch removes Performance and AnimationValue now that we've ported the
framework over to AnimationController and Tween. This patch also cleans up the
names of the AnimationController classes now that they don't have to avoid
conflicts with the old animation API. Specifically, I've made the following
renames:

 * Animated -> Animation
 * Evaluatable -> Animatable
 * PerformanceStatus -> AnimationStatus

This patch is just renames and moving code around. There aren't any changes in
behavior.

Providing a pre-built child is more efficient because we don't need to rebuild
the child every tick of the animation.

Also, clean up the class hierarchy for AnimationController now that
we've renamed progress to value. That means everything in the hierarchy
now has a value, include Watchable. This patch renames Watchable to
Animated<T>, which lets us use that type almost everywhere.

I've added some ducktape to modal bottom sheets to avoid having to
refactor all of Navigator to use AnimationController. I'll remove the
ducktape in the next patch.

Previously we used a positional argument for widgets that had multiple
children. Now we use a named argument that defaults to an empty list.

Fixes #241

Also, replace places that use the term "create performance" with
"create performance controller".

- `Scaffold.of(context).showBottomSheet(widget);`
- Returns an object with .closed Future and .close() method.
- Uses a StateRoute to handle back button.
- Take the Navigator logic out of the BottomSheet widget.
- Support showing a sheet while an old one is going away.
- Add Navigator.remove().

"showSnackBar()" is now a feature of a Scaffold. To get to a Scaffold
you either use a global key (`scaffoldKey.currentState.showSnackBar(...)`),
or you use `Scaffold.of(context)`.

Snack bars no longer have a route. They are entirely managed by the
Scaffold. Fixes #432.

Snack bars now queue up when you have several of them. Fixes #374.

Snack bars now auto-size themselves around their contents. This is step
one towards implementing multiline snack bars.

Snack bars now self-dismiss after some per-snackbar configurable period.

The self-dismissing pauses while a dialog is up above the snackbar (or
anything that uses ModalRoute). To enable this, there's now a
`ModalRoute.of(context)` API that returns the current ModalRoute, and
you will be rebuilt if you asked for this and the route's "current"
status changes. To implement this, the Navigator now rebuilds
unconditionally any time it pushes or pops a route.

Snack bars now use the curves that Android uses for snack bars.

Snack bar contents now fade in.

Shadows now render as three seprate MaskFilter.blur components per the most recent Material spec.

The shadows Map was replaced by a similar Map called elevationToShadow with entries that match the 10 elevations specifed by http://www.google.com/design/spec/what-is-material/elevation-shadows.html.

The "level" property (many classes) is now called "elevation", to match the Material spec.

BoxShadow now includes a spreadRadius parameter - as in CSS box-shadow. Renamed the BoxShadow blur property to blurRadius to further align BoxShadow with CSS box-shadow.