This should reduce the risk of running out of cache entries inside a frame, while being small enough that iterating through it to find the correct entry shouldn't be too expensive.

BUG=310
TEST=

Review URL: https://codereview.appspot.com/5969077

git-svn-id: https://angleproject.googlecode.com/svn/trunk@1018 736b8ea6-26fd-11df-bfd4-992fa37f6226