Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

mojo/gpu/mojo_gles2_impl_autogen.h

 // 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 817 matching lines @@
   void StencilThenCoverFillPathCHROMIUM(GLuint path,
                                         GLenum fillMode,
                                         GLuint mask,
                                         GLenum coverMode) override;
   void StencilThenCoverStrokePathCHROMIUM(GLuint path,
                                           GLint reference,
                                           GLuint mask,
                                           GLenum coverMode) override;
   GLenum GetGraphicsResetStatusKHR() override;
   void BlendBarrierKHR() override;
+  void ApplyScreenSpaceAntialiasing() override;
 
  private:
   MojoGLES2Context context_;
 };
 
 }  // namespace mojo
 #endif  // MOJO_GPU_MOJO_GLES2_IMPL_AUTOGEN_H_