WIP Handle AwContents needing multiple live functors.

android_webview/browser/compositor_frame_consumer.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_CONSUMER_H_
 #define ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_CONSUMER_H_
 
 #include <map>
 
 #include "android_webview/browser/parent_compositor_draw_constraints.h"
 #include "cc/resources/returned_resource.h"
 #include "ui/gfx/geometry/vector2d.h"
 
 namespace android_webview {
 
 class ChildFrame;
 class CompositorFrameProducer;
 
 class CompositorFrameConsumer {
  public:
   struct ReturnedResources {
     ReturnedResources();
     ~ReturnedResources();
 
     uint32_t output_surface_id;
     cc::ReturnedResourceArray resources;
   };
   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;
   virtual void SetFrameOnUI(std::unique_ptr<ChildFrame> frame) = 0;
   virtual void InitializeHardwareDrawIfNeededOnUI() = 0;
   virtual ParentCompositorDrawConstraints GetParentDrawConstraintsOnUI()
       const = 0;
   virtual void SwapReturnedResourcesOnUI(
       ReturnedResourcesMap* returned_resource_map) = 0;
   virtual bool ReturnedResourcesEmptyOnUI() const = 0;
   virtual std::unique_ptr<ChildFrame> PassUncommittedFrameOnUI() = 0;
   virtual bool HasFrameOnUI() const = 0;
   virtual void DeleteHardwareRendererOnUI() = 0;
 
  protected:
   virtual ~CompositorFrameConsumer() {}
 };
 
 }  // namespace android_webview
 
 #endif  // ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_PRODUCER_H_