GitLab

 The last mouse location should be the updated only by real event because it should point to the real mouse point and synthesized enter/leave may not contain the valid point.

minor: remove unnecessary cast.

BUG=None
TEST=TBD.

Review URL: https://codereview.chromium.org/143303006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251291 0039d316-1c4b-4281-b951-d872f2087c98