Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

mojo/gpu/mojo_gles2_impl_autogen.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file is auto-generated from
 // gpu/command_buffer/build_gles2_cmd_buffer.py
 // It's formatted by clang-format using chromium coding style:
 //    clang-format -i -style=chromium filename
 // DO NOT EDIT!
 
@@ skipping 1703 matching lines @@
                                                        GLenum coverMode) {
   NOTREACHED() << "Unimplemented StencilThenCoverStrokePathCHROMIUM.";
 }
 GLenum MojoGLES2Impl::GetGraphicsResetStatusKHR() {
   NOTREACHED() << "Unimplemented GetGraphicsResetStatusKHR.";
   return 0;
 }
 void MojoGLES2Impl::BlendBarrierKHR() {
   NOTREACHED() << "Unimplemented BlendBarrierKHR.";
 }
+void MojoGLES2Impl::ApplyScreenSpaceAntialiasingCHROMIUM() {
+  NOTREACHED() << "Unimplemented ApplyScreenSpaceAntialiasingCHROMIUM.";
+}
 
 }  // namespace mojo