Use a minimum touch size for selection handle hit testing

Use a minimum touch size for selection handle hit testing

Certain Android devices, as well as stylus and mouse inputs, may report zero
for the touch size. These sizes are used when constructing the rect for touch
handle insersection tests.  However, gfx::RectBase will always report false when
performing the intersection test if either rect is empty.  Add an appropriate
epsilon minimum touch size when forming the touch bounding box rect.

BUG=402795
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289501

[jdduke (slow), 2014-08-12 18:45:58]

cjhopman@: PTAL, thanks.  Didn't realize this until inspecting the
RectBase::Intersect source code. I also reduced the max touch size based on some
informal testing; 48 seemed to register more "phantom" touch hits than proper on
certain Sony devices.

[cjhopman, 2014-08-13 23:31:09]

lgtm

[jdduke (slow), 2014-08-13 23:40:01]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-08-13 23:45:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jdduke@chromium.org/462163002/1

[commit-bot: I haz the power, 2014-08-14 09:41:31]

Committed patchset #1 (1) as 289501