aura: Start updating aura to use EventProcessor for event dispatch.

aura: Start updating aura to use EventProcessor for event dispatch.

Notable changes in this CL:
 * A WindowTargeter implementation for finding the target Window for an event
   (currently unused), with only a most basic test.
 * Make RootWindow a ui::EventProcessor.
 * Make RootWindowHostX11 a ui::EventSource.

Note that RootWindowHostX11 continues to dispatch events to the RootWindow using
RootWindowHostDelegate interface. This CL prepares much of the machinery for
switching to EventProcessor interface for event dispatch, but it is essentially a
no-op for now.

BUG=318879
[email protected]

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=239277

[Ben Goodger (Google), 2013-12-06 18:23:54]

lgtm

[sadrul, 2013-12-06 23:55:55]

Committed patchset #1 manually as r239277 (presubmit successful).