Fixes #692
Fixes #690

Add custom clipping to ClipRect and ClipOval

Add the ability to custom paint foregrounds

Add script for profiling startup using flutter trace on Android

Slider Improvements

Have the widget support min/max arguments to make the widget easier to
use. Also, fix the dragging so it's actually where the knob is.

This will work after the next Engine roll.  Currently it requires
a fix to tracing which isn't in the released engine.

Next steps are to make this work on a bot, and to add iOS support.

@abarth @chinmaygarde

Example of using the Dart internationalization package in Flutter

Improve material ink response

This patch contains a number of improvements to the material ink response:

- The ink response now remains until you lift your finger
- When disappearing, the ink response now fades out
- The ink response is now the correct color (at least in the light theme)
- The ink response for IconButton now has a (circular) highlight
- The ink response for IconButton now repositions itself to be centered on the highlight

In addition, I've adjusted the various animation parameters to better match the
behavior of ink responses in the Java implementation of material.

Fixes #695

Introduce some basic utility classes.

Analyzer improvements

One might argue, the most basic utility classes.

- strengthen analyzer against error messages that point past the
  bottom of the file.

- ignore any errors in intl's auto-generated files.

Automatically fill in the menu button when there's a drawer

Add support for letterSpacing to TextStyle

Also, fill in a back arrow when we can go back.

Fixes #699

Workaround logcat -c not working

Be more discerning with forward transitions

Allow non-Material apps to use the Title widget.

Navigator.canPop(context)

So you don't fade out when going to a popup menu, for example.

Make it possible to specify the saved path for trace --stop

@chinmaygarde

RenderFlex shouldn't assert when its out of space

Let MaterialApp.onGenerateRoute return a Route

Add menu items to stocks to control timeDilation

Previously, we would assert with FlexJustifyContent.collapse if we ran out of
space. Now we do the same thing we do for the other types of justification,
which is to let the children's layout overflow.

Also:
 - minor code reindents in places.
 - reset the widget tree between tests.
 - once you generate a route, don't let its builder change
   (previously it would keep changing as the routes table changed).
 - revert the stocks app toolbar-fading-on-forward-transition thing.

Add support for passing --trace-startup on Android