Adds switch to disable generating mouse events from touch events and

Adds switch to disable generating mouse events from touch events and
adds tracking of whether any touch devices are down. I'm going to use
the later from Widget.

BUG=113279
TEST=none
R=sadrul@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=139891

[sadrul, 2012-05-31 18:59:27]

LGTM

http://codereview.chromium.org/10448102/diff/1/ui/aura/root_window.cc
File ui/aura/root_window.cc (right):

http://codereview.chromium.org/10448102/diff/1/ui/aura/root_window.cc#newcode320
ui/aura/root_window.cc:320: touch_ids_down_ = (touch_ids_down_ | (1 <<
event->touch_id())) ^
Does it make sense to have a DCHECK here for (touch_ids_down_ & (1 <<
event->touch_id()))?

[sky, 2012-05-31 19:41:44]

As mentioned in IM I couldn't use a DCHECK since some tests generate events in a
non-typical pattern. I did remove handling of CANCELLED though, since it appears
we're guaranteed to get a RELEASE.
Additionally it seemed as though GestureRecognizerImpl::CancelNonCapturedTouches
would generate more ET_TOUCH_CANCELLEDs then necessary. Specifically it was
possible to get two cancelled events.
Take another look?

[sadrul, 2012-05-31 22:18:29]

LGTM (sorry for the delayed review)