Delegate root layer scroll offset to android_webview.

content/renderer/gpu/input_handler_manager.h

Index: content/renderer/gpu/input_handler_manager.h
diff --git a/content/renderer/gpu/input_handler_manager.h b/content/renderer/gpu/input_handler_manager.h
index c33b5b772fdc75b8872145bcc109917a17a3c1cd..5206664ca654c04b5c24e1fd8db565ea167a1700 100644
--- a/content/renderer/gpu/input_handler_manager.h
+++ b/content/renderer/gpu/input_handler_manager.h
@@ -17,6 +17,7 @@ class MessageLoopProxy;
 
 namespace cc {
 class InputHandler;
+class LayerScrollOffsetDelegate;
 }
 
 namespace WebKit {
@@ -51,6 +52,13 @@ class InputHandlerManager {
       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);