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This allows touch devices to be grabbed when events from the mouse/keyboard are
grabbed. This also exposes TouchFactory, which will eventually be used in more
places.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6300007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71879 0039d316-1c4b-4281-b951-d872f2087c98