Implement GL_KHR_debug.

BUG=angleproject:520

Change-Id: I9ced3e7ab1515feddf2ec103c26b2610a45b1784
Reviewed-on: https://chromium-review.googlesource.com/319830
Tryjob-Request: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index e9cd516..1784bba 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -109,9 +109,15 @@
       case GL_BLEND:
       case GL_DITHER:
         return true;
+
       case GL_PRIMITIVE_RESTART_FIXED_INDEX:
       case GL_RASTERIZER_DISCARD:
         return (context->getClientVersion() >= 3);
+
+      case GL_DEBUG_OUTPUT_SYNCHRONOUS:
+      case GL_DEBUG_OUTPUT:
+          return context->getExtensions().debug;
+
       default:
         return false;
     }