Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

mojo/gpu/mojo_gles2_impl_autogen.cc

Index: mojo/gpu/mojo_gles2_impl_autogen.cc
diff --git a/mojo/gpu/mojo_gles2_impl_autogen.cc b/mojo/gpu/mojo_gles2_impl_autogen.cc
index 323a936a333e9dd3a0117f859d835baf992d59da..ad568842ecc140fb55336c72df57c048134979b9 100644
--- a/mojo/gpu/mojo_gles2_impl_autogen.cc
+++ b/mojo/gpu/mojo_gles2_impl_autogen.cc
@@ -825,7 +825,8 @@ void MojoGLES2Impl::ShallowFlushCHROMIUM() {
   glShallowFlushCHROMIUM();
 }
 void MojoGLES2Impl::OrderingBarrierCHROMIUM() {
-  NOTREACHED() << "Unimplemented OrderingBarrierCHROMIUM.";
+  MojoGLES2MakeCurrent(context_);
+  glOrderingBarrierCHROMIUM();
 }
 void MojoGLES2Impl::StencilFunc(GLenum func, GLint ref, GLuint mask) {
   MojoGLES2MakeCurrent(context_);
@@ -1748,5 +1749,8 @@ GLenum MojoGLES2Impl::GetGraphicsResetStatusKHR() {
 void MojoGLES2Impl::BlendBarrierKHR() {
   NOTREACHED() << "Unimplemented BlendBarrierKHR.";
 }
+void MojoGLES2Impl::ApplyScreenSpaceAntialiasing() {
+  NOTREACHED() << "Unimplemented ApplyScreenSpaceAntialiasing.";
+}
 
 }  // namespace mojo