Add command buffer support for GL_RGB CHROMIUM image emulation.

ui/gl/gl_image.h

Index: ui/gl/gl_image.h
diff --git a/ui/gl/gl_image.h b/ui/gl/gl_image.h
index 6b98fe995b8127d26fd47191959c56a6a09ec59f..929970ea9e43b35546cf62284012e1640f65b3a5 100644
--- a/ui/gl/gl_image.h
+++ b/ui/gl/gl_image.h
@@ -74,6 +74,17 @@ class GL_EXPORT GLImage : public base::RefCounted<GLImage> {
                             uint64_t process_tracing_id,
                             const std::string& dump_name) = 0;
 
+  // If this returns true, then the command buffer client has requested a
+  // CHROMIUM image with internalformat GL_RGB, but the platform only supports
+  // GL_RGBA. The client is responsible for implementing appropriate
+  // workarounds. The only support that the command buffer provides is format
+  // validation during calls to copyTexImage2D and copySubTexImage2D.
+  //
+  // This is a workaround that is not intended to become a permanent part of the
+  // GLImage API. Theoretically, when Apple fixes their drivers, this can be
+  // removed. https://crbug.com/581777#c36
+  virtual bool EmulatingRGB() const;
+
  protected:
   virtual ~GLImage() {}