Add a simple scheduler for animation frames

Add a simple scheduler for animation frames

This CL adds a simple scheduler for animation frames that holds a given interval
in a given phase.  The scheduler can be told the estimated duration of the
BeginFrame callback and can adjust the callback to hit a given vsync interval.

This CL also makes ganesh_app use this scheduler to animate.

R=jamesr@chromium.org, ernstm@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/d6f119dea629ee005e03f32a5e025e7d940e25c7

[abarth-chromium, 2014-11-16 05:49:12]

abarth@chromium.org changed reviewers:
+ ernstm@chromium.org

[abarth-chromium, 2014-11-16 06:00:27]

This CL is based on the cc/scheduler, but without all the abstraction and
complexity.  In particular, we don't support a high-resolution time source
because that appears to exist only on windows.  Also, we don't need to support
the N different phases in cc (e.g., CalcDrawProps).  Presumably mc/scheduler
will get more complicated over time as we add more phases, but for now it looks
like we can use something relatively simple.

Let me know what you think.

[jamesr, 2014-11-17 18:40:13]

lgtm but put this somewhere under sky/

[abarth-chromium, 2014-11-17 19:24:12]

Committed patchset #4 (id:60001) manually as
d6f119dea629ee005e03f32a5e025e7d940e25c7 (presubmit successful).

[abarth-chromium, 2014-11-17 19:24:57]

Moved to sky/scheduler

Also, dropped the changes to ganesh_app