Cherry-pick WebKit change r77191 to pick up a rendering optimization

The primary motivation for taking this change is to allow r100677 to be
cherry-picked cleanly. It should introduce no functional change.

See http://trac.webkit.org/changeset/77191

Bug: 6079158
Change-Id: Ica1904db507b2fa8beda8d6c208470c35e4f7b19
3 files changed