A NestedScrollView lets you implement patterns where you have a header, tabs,
and additional scrollers inside the tabs.

Fixes #8359

* make @immutable const

* fix build

Aggressively apply the const lint.

This machinery is useful for arbitrary boxes (e.g., with FittedBox).

Fixes #6463

* Add cupertino to gallery and add CupertinoButto

* Use single quotes

* Add disabled state

* Some review notes

* Make button animation more responsive and tweak timing

* Renamed things Cupertino

* Button with background, move cupertino demos, move material demos

* Move 2 level list too

* Refactor various demo route names

* Some review notes

* More reviews and add test

* Linter as

* Move private constant up

This prepares us for a CustomScrollView that takes slivers.

Now that ScrollView supports itemExtent, we can use it in a few more places.

These now have sorter names to make the callers less verbose.

Some folks didn't realize these existed and asked us to add them. By
using them in examples, hopefully folks will discover them more easily.

Looks like our intent here was to show the tab label rather than
"Instance of '_Page'".

Also, fix an issue where the scrollableKey wasn't being forwarded to the
actual scrollable.

Fixes #3090

Use the route table to generate the list of screens to test in the smoke test.

* Remove Scaffold scrollable_key demo usage

See https://www.google.com/design/spec/style/writing.html#

Now MediaQuery.of always returns a non-null value. By default, you get the
values associated with the current ui.Window.

Fixes #2894

* left -> leading (Removes an LTR bias)
* center -> title (Widget was actually centered)
* right -> actions (Removes an LTR bias, asymmetric with leading)

Fixes #2348

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #1382

And fix the zillion issues that uncovered.

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

And fix the zillion issues that uncovered.

Rather than managing all the Material Design icons manually, we now
manage them using an icon font. The icon font contains glyphs for each
icon in an efficient vector format.

This patch updates the FLX tooling to include the MaterialIcons font and
updates the Icon widget to use the font instead of asset images.

Fixes #2313
Fixes #2218
Fixes #2009
Fixes #994

Instead of taking a builder and a generic type, we can just take a
List<Widget>.

This patch moves PageableList off HomogeneousViewport and onto RenderList and
friends, making it match the new ScrollableList.

The TabBarSelection change animation needs to start where the fling's drag gesture ended rather than from zero.  The intial vlaue of progress for the TabBarSelection's performance is now converted from the range used during an interactive drag, to the range used when animating from the previously selected tab to the new one.

TabBarSelection now requires a maxIndex parameter.