Modify hit test masks for tabs and tab close buttons

In preparation for landing rect-based event targeting 
(issue 129794), the tab close button will need a hit 
test mask and the hit test mask for a tab will need 
to be modified. This will take into consideration the 
possibility where the tab close button of one tab is 
occluded by another tab when in stacked tab / touch 
layout mode.

BUG=306186
TEST=TabStripTest.TabHitTestMaskWhenStacked

Review URL: https://codereview.chromium.org/32463003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232797 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed