Clamp the hotspot on custom cursors to the custom cursor image.

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

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=55669

[Evan Martin, 2010-08-11 00:01:58]

LGTM

http://codereview.chromium.org/3168003/diff/1/4
File webkit/glue/webcursor_unittest.cc (right):

http://codereview.chromium.org/3168003/diff/1/4#newcode105
webkit/glue/webcursor_unittest.cc:105:
ASSERT_TRUE(custom_cursor.Deserialize(&ok_custom_pickle, &iter));
yay correct usage of assert

[darin (slow to review), 2010-08-14 06:46:16]

LGTM2