cc: Implement deadline scheduling disabled by default

cc: Implement deadline scheduling disabled by default

This patch adds logic to the Scheduler to actually use the BeginFrame
and deadline, but is not enabled by default on any platform yet. This
will ensure emulation of old scheduler in the fallback path is sane.
Emulation of the old path is implemented using an immediate deadline.

SchedulerStateMachine::begin_frame_state has been added and can be in one
of 4 states: Idle, InsideBeginFrame, DeadlinePending, or InsideDeadline.

Notable restrictions of the states are:
- We start a commit as soon after InsideBeginFrame as we can, since the
BeginFrame will be coordinated with user input. (True on Android.
Soon to be true on other platforms.)
- We do not start a commit while Idle, in order to wait for the next
batch of user input.
- Draw and swap only occurs during the InsideDeadline state.

The deadlines of the Browser and Renderer compositors can be nested in
order to have a total draw latency of < 1 frame when starting off. If we
can't hit 1 frame of latency consistently, we will fallback to a higher
latency mode to increase throughput.

BUG=243461

[brianderson, 2013-09-20 00:46:21]

To be both safe and simple in the latest patch, I do not block the commit in
BEGIN_FRAME_IDLE if deadline scheduling is disabled. This replicates ToT
behavior almost exactly.

I've modified the necessary Scheduler tests that need deadline and non-deadline
versions already.

We might want to modify the LayerTreeHost unit tests with a deadline flag as
well. However, considering this is going in disabled by default everywhere
first, I would like to land this patch before the LTH unit test changes.

[brianderson, 2013-09-20 18:01:47]

Base files missing still. Moved again to:
https://codereview.chromium.org/24070006