WIP Handle AwContents needing multiple live functors.

android_webview/browser/compositor_frame_consumer.h

Index: android_webview/browser/compositor_frame_consumer.h
diff --git a/android_webview/browser/compositor_frame_consumer.h b/android_webview/browser/compositor_frame_consumer.h
index 4542d2aa4c421d58af75015c64a6a312222c67fb..b5b7595a359ed9de912c48dc630097f768edabed 100644
--- a/android_webview/browser/compositor_frame_consumer.h
+++ b/android_webview/browser/compositor_frame_consumer.h
@@ -27,8 +27,15 @@ class CompositorFrameConsumer {
   };
   using ReturnedResourcesMap = std::map<uint32_t, ReturnedResources>;
 
+  // A CompositorFrameConsumer may be registered with at most one
+  // CompositorFrameProducer.  The producer is responsible for
+  // managing the relationship with its consumers. In order to
+  // register a consumer with a new producer, the current producer
+  // must first unregister the consumer, and call
+  // SetCompositorProducer(nullptr).
   virtual void SetCompositorFrameProducer(
       CompositorFrameProducer* compositor_frame_producer) = 0;
+
   virtual void SetScrollOffsetOnUI(gfx::Vector2d scroll_offset) = 0;
   virtual void SetFrameOnUI(std::unique_ptr<ChildFrame> frame) = 0;
   virtual void InitializeHardwareDrawIfNeededOnUI() = 0;