Complete disable_gl_rgb_format workaround for Mali-400 GPU

gpu/command_buffer/service/context_state.h

Index: gpu/command_buffer/service/context_state.h
diff --git a/gpu/command_buffer/service/context_state.h b/gpu/command_buffer/service/context_state.h
index 5a58916e93e8701864e8a8d210773499de42dd9a..868867808e00930d262a506e7327902d38125031 100644
--- a/gpu/command_buffer/service/context_state.h
+++ b/gpu/command_buffer/service/context_state.h
@@ -209,7 +209,7 @@ struct GPU_EXPORT ContextState {
     cached_color_mask_green = green;
     cached_color_mask_blue = blue;
     cached_color_mask_alpha = alpha;
-    glColorMask(red, green, blue, alpha);
+    glColorMask(red, green, blue, emulating_rgb_with_rgba ? false : alpha);
   }
 
   inline void SetDeviceDepthMask(GLboolean mask) {
@@ -294,6 +294,8 @@ struct GPU_EXPORT ContextState {
 
   mutable bool fbo_binding_for_scissor_workaround_dirty;
 
+  bool emulating_rgb_with_rgba;
+
  private:
   void EnableDisable(GLenum pname, bool enable) const;
 
@@ -314,4 +316,3 @@ struct GPU_EXPORT ContextState {
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_CONTEXT_STATE_H_
-