Added support for EXT_frag_depth

This change also required that support be added for associating built-in
variables with an extension, similar to how functions could be associated with
extensions previously.

R=alokp@chromium.org

Review URL: https://codereview.appspot.com/9827044

git-svn-id: https://angleproject.googlecode.com/svn/trunk@2248 736b8ea6-26fd-11df-bfd4-992fa37f6226

TRAC #23333
Authored-by: bajones@chromium.org
Signed-off-by: Shannon Woods
Signed-off-by Nicolas Capens
Merged-by: Jamie Madill
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index 871e566..03470e9 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -3026,6 +3026,7 @@
         }
 
         mExtensionStringList.push_back("GL_EXT_texture_storage");
+        mExtensionStringList.push_back("GL_EXT_frag_depth");
 
         // ANGLE-specific extensions
         if (supportsDepthTextures())