Fix a UMR that happens while trying to forward mouse events.

The input param gets clobbered so we need to make a copy before
using it.

TEST=Run chrome via valgrind and move the mouse over the content area.  There
  should be no errors.

Review URL: http://codereview.chromium.org/126081


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@18404 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed