this optimization level, it appears that array index clamping can be
enabled on Windows without destabilizing WebGL content.

Tested this change with array index clamping enabled with MapsGL, a
previous failing test from AlteredQualia, many Three.js demos, the
Julia Set tutorial from acko.net, the WebGL 1.0.1 conformance suite,
and other content; all worked.

BUG=none
Review URL: https://codereview.appspot.com/7197054

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1799 736b8ea6-26fd-11df-bfd4-992fa37f6226