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/compiler/ShaderLang.cpp b/src/compiler/ShaderLang.cpp
index efdcb67..edfb3f8 100644
--- a/src/compiler/ShaderLang.cpp
+++ b/src/compiler/ShaderLang.cpp
@@ -127,6 +127,7 @@
     resources->OES_EGL_image_external = 0;
     resources->ARB_texture_rectangle = 0;
     resources->EXT_draw_buffers = 0;
+    resources->EXT_frag_depth = 0;
 
     // Disable highp precision in fragment shader by default.
     resources->FragmentPrecisionHigh = 0;