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..311186800268823d730557baa29c73212750f488 100644
--- a/android_webview/browser/compositor_frame_consumer.h
+++ b/android_webview/browser/compositor_frame_consumer.h
@@ -27,6 +27,13 @@ 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. The only exception to this is when a consumer is explicitly
+  // destroyed, at which point it needs to inform its producer.
+  // In order to register a consumer with a new producer, the current producer
+  // must unregister the consumer, and call SetCompositorProducer(nullptr).
   virtual void SetCompositorFrameProducer(
       CompositorFrameProducer* compositor_frame_producer) = 0;
   virtual void SetScrollOffsetOnUI(gfx::Vector2d scroll_offset) = 0;