Clamp the hotspot on custom cursors to the custom cursor image's dimensions.

Current behavior:
windows chrome - respect the crazy hotspot
linux chrome - crash
mac chrome - fall back to normal cursor
firefox - clamp the hotspot to the custom cursor image bounds.

So this unifies the behavior of all 3 chrome platforms and matches firefox.

BUG=51709
TEST=see bug for reduction

Review URL: http://codereview.chromium.org/3168003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@55669 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed