Refactors randomizations of color sequences and optimizes particle systems (uses single Paint instance, doesn't compute accelerations unless used, reduces number of created objects, faster color calculations)
Fixes indentation
Optimizes lookup in fast version of atan2 (toInt is faster than floor)
Removes frame rate printout and adds assert

Conflicts:
	sky/sdk/example/game/lib/particle_system.dart

Use Skia's drawAtlas now that we've rolled to a newer Skia

Roll was ff8bbe4e1674ae57f2ea3a2841a37a9c099beac8
This is another step in fixing #138

R=viktork@google.com

Turns out if we don't have these deps, nothing builds these packages.

We now just symlink the lib directory into the packages directory in the output
directory.

This package contains the mojom.dart files we generate from the sky_engine
repository.

Move Material Design Icons to their own package

After this patch, we use pub to manage versioning and fetching the material
design icons.

Adds test case for drawAtlas in games

Add a dialog to the address book app to test scoped focus.

Add a sky_engine package to contain the dart:sky SDK extensions

Create a SkyShell.apk

Adds custom play button with texture to demo game

This CL introduces a SkyShell.apk that is separate from the SkyDemo.apk that we
upload to the store to show our demos.  The SkyShell.apk is just an empty shell
that can run Sky applications on Android.

I've noticed an anti-pattern emerge where people call scheduleBuild()
when they think they've changed enough state that they should rebuild,
instead of just wrapping their changes in setState(). This leads to
them missing state changes, having extraneous scheduleBuild() calls,
and other similar bugs.

By removing scheduleBuild(), the only way to actually schedule a build
now is to call setState(), and hopefully that'll make it much clearer
that you're only supposed to do this when you change state.

Assert that there are no duplicates.
Export GlobalKey from basic.dart, so that people don't have to import widgets.dart just for that.
Fix the "initialFocus" feature which actually didn't work.

Switch sky_tool to use a Dart-based HTTP server

This is supposed to make Viktor's game faster, but it's not clear
to me that it actually does.  I've left the code
using the dart version of drawAtlas for now until Viktor can
verify that it looks correct.

I also added a wrapper for SkFilterQuality in the process of
debugging SkCanvas.drawAtlas since all drawAtlas examples
in Skia use FilterQuality.low.  The bug which blocked me for
so long turned out to be that SkCanvas.drawAtlas doesn't
draw anything if antialiasing is turned on.

Issue #138.

R=abarth@google.com

RenderConstrainedBox was ignoring its additional constraints for its intrinsic size logic when it had no child.

Fix analyzer warnings

 - Remove unused imports
 - Remove unused, broken constructor for MineDiggerApp

This patch provides a class to manage focus, Focus, and a class to
manage ownership of the keyboard, KeyboardHandle.

Inherited (in widgets.dart) is adjusted to support subclasses that
need to copy state from instance to instance.

A GlobalKey key type is introduced that is basically the same as
UniqueKey. Component classes that need a globally-unique key can
specify that their 'key' constructor argument is a GlobalKey.

Focus
-----

You can use `Focus.at(this)` to determine if you, a Component, are
currently focused.

You can use `Focus.moveTo(this)` to take the focus or give it to a
particular component.

For this to work, there has to be a Focus class in the widget
hierarchy.

Currently, there can only be one Focus class, because nested scopes
aren't supported. We should add support for that in a future patch.
See issue #229.

KeyboardHandle
--------------

Instead of directly interacting with the keyboard service, you now ask
for a KeyboardHandle using `_keyboard.show(client)`. This returns a
KeyboardHandle class. On that class, you can call `handle.release()`
when you want to hide the keyboard. If `handle.attached` is still
true, and you need to reshow the keyboard after the user hid it, then
you can can `handle.showByRequest()`.

The point of this is that the `keyboard.show()` method maintains the
invariant that only one KeyboardHandle is live at a time.

There are some issues with the keyboard service that I filed as a
result of doing this patch: #226 #227

Accessing the network created a race condition that would sometimes cause other
tests to fail.

The Python HTTP server was caching too agressively. Instead, use an HTTP server
written in Dart from the sky_tools package.

Fix the crash when going to settings after showing the popup menu.