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 41970899098cb5533b9ef038b66221c0965ab5d0..ce84596ad2f5e9fe002442169b8c32b2aa154afc 100644
--- a/mojo/gpu/mojo_gles2_impl_autogen.h
+++ b/mojo/gpu/mojo_gles2_impl_autogen.h
@@ -890,6 +890,7 @@ 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;