When the user right-clicks on the new tab button in the tab strip, show the tab strip context menu.
When the user right-clicks on the new tab button in the tab strip, show the
tab strip context menu.

BUG=81221
TEST=Right click on the new tab button and make sure the context menu appears.
Make sure to click inside the button's irregular shape.

Review URL: http://codereview.chromium.org/8386052

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@109061 0039d316-1c4b-4281-b951-d872f2087c98

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