Delegate root layer scroll offset to android_webview.

content/renderer/gpu/input_handler_manager.h

 // Copyright (c) 2012 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 CONTENT_RENDERER_GPU_INPUT_HANDLER_MANAGER_H_
 #define CONTENT_RENDERER_GPU_INPUT_HANDLER_MANAGER_H_
 
 #include <map>
 
 #include "base/memory/weak_ptr.h"
 #include "content/renderer/render_view_impl.h"
 #include "ipc/ipc_channel_proxy.h"
 
 namespace base {
 class MessageLoopProxy;
 }
 
 namespace cc {
 class InputHandler;
+class LayerScrollOffsetDelegate;
 }
 
 namespace WebKit {
 class WebInputEvent;
 }
 
 namespace content {
 
 class InputEventFilter;
 class InputHandlerWrapper;
@@ skipping 14 matching lines @@
   // This MessageFilter should be added to allow input events to be redirected
   // to the compositor's thread.
   IPC::ChannelProxy::MessageFilter* GetMessageFilter() const;
 
   // Callable from the main thread only.
   void AddInputHandler(
       int routing_id,
       const base::WeakPtr<cc::InputHandler>& input_handler,
       const base::WeakPtr<RenderViewImpl>& render_view_impl);
 
+  // Called from the compositor's thread.
+  // |layer_scroll_delegate| will be accessed from the Compositor Impl thread
+  // and must outlive the InputHandler that it's associated with.
+  void SetRootLayerScrollDelegate(

[joth, 2013/06/01 02:11:35]

@jdduke - any comments on duplicating this cc::InputHandler method on
InputHandlerManager? Alternatives could be:
1 - a getter here:  cc::InputHandler* GetHandler(int routing_id)
2 - pushing it up the otherway:
 a) InputHandlerManagerClient::DidCreate/DestoryInputHandler(int routing_id,
cc::InputHandler*)
 b) cc::LayerScrollOffsetDelegate*
InputHandlerManagerClient::GetScrollOffsetDelegate(int routing_id)
 c) InputHandlerManagerClient::Get/SetTotalRootLayerScrollOffset()


#2 has threading and lifetime questions. might need a new
LayerScrollOffsetDelegate::DidDestroyInputHandler() call or something.
2(c) ends up duplicating the cc::LayerScrollOffsetDelegate::Xxx methods onto
three different interfaces...


hmmm even after this patch, we also need to connect the call from
SynchronousCompositorImpl down to
InputHandler::OnRootLayerDelegatedScrollOffsetChanged()

so, with ref to
https://codereview.chromium.org/15920002/diff/53001/content/renderer/gpu/inpu...
it seems like 
3/ the 'Handler' typedef could be expanded to a full interface and host the
three methods (HandleEvent, SetRootScrollDelegate,
OnRootLayerDelegatedScrollOffsetChanged) we'd be good.
OR
4/ can we somehow skip past InputHandlerManager and InputHandlerWrapper and
somehow get straight to the appropriate InputHandler instance from 
SynchronousCompositorImpl? Then we'd be golden for all three method calls.

+      int routing_id,
+      cc::LayerScrollOffsetDelegate* root_layer_scroll_offset_delegate);
+
   // Callback only from the compositor's thread.
   void RemoveInputHandler(int routing_id);
 
   // Called from the compositor's thread.
   void HandleInputEvent(int routing_id,
                         const WebKit::WebInputEvent* input_event);
 
   // Called from the compositor's thread.
   InputEventFilter* filter() { return filter_.get(); }
 
  private:
   // Called from the compositor's thread.
   void AddInputHandlerOnCompositorThread(
       int routing_id,
       const scoped_refptr<base::MessageLoopProxy>& main_loop,
       const base::WeakPtr<cc::InputHandler>& input_handler,
       const base::WeakPtr<RenderViewImpl>& render_view_impl);
 
   typedef std::map<int,  // routing_id
                    scoped_refptr<InputHandlerWrapper> > InputHandlerMap;
   InputHandlerMap input_handlers_;
 
   scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
   scoped_refptr<InputEventFilter> filter_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_INPUT_HANDLER_MANAGER_H_