command_buffer: Implement CHROMIUM_framebuffer_mixed_samples extension

mojo/gpu/mojo_gles2_impl_autogen.h

Index: mojo/gpu/mojo_gles2_impl_autogen.h
diff --git a/mojo/gpu/mojo_gles2_impl_autogen.h b/mojo/gpu/mojo_gles2_impl_autogen.h
index c00372ddbe1b7a004ad52b62b89b2ab41dabe76b..872560940263ad49bf0d66ce586cc60b09e8ac19 100644
--- a/mojo/gpu/mojo_gles2_impl_autogen.h
+++ b/mojo/gpu/mojo_gles2_impl_autogen.h
@@ -885,6 +885,7 @@ class MojoGLES2Impl : public gpu::gles2::GLES2Interface {
                                            GLenum genMode,
                                            GLint components,
                                            const GLfloat* coeffs) override;
+  void CoverageModulationCHROMIUM(GLenum components) override;
   GLenum GetGraphicsResetStatusKHR() override;
   void BlendBarrierKHR() override;
   void ApplyScreenSpaceAntialiasingCHROMIUM() override;