We were setting the max vertex way too low, causing AMD cards to draw the line with an incorrect vertex.

BUG=
TEST=enable "Composited render layer borders" in chromium

Review URL: http://codereview.appspot.com/4588042

git-svn-id: https://angleproject.googlecode.com/svn/trunk@691 736b8ea6-26fd-11df-bfd4-992fa37f6226