Plumb an overscroll callback form the compositor to the Android UI thread.

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index 0b36fdc07f98fe85a2da382ce9ddbf5846299963..1c89ae834ff47db96025a55bece71428186685e1 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -696,6 +696,15 @@ IPC_STRUCT_BEGIN(ViewMsg_New_Params)
   IPC_STRUCT_MEMBER(AccessibilityMode, accessibility_mode)
 IPC_STRUCT_END()
 
+IPC_STRUCT_BEGIN(ViewHostMsg_UpdateFrameInfo_Params)

[aelias_OOO_until_Jul13, 2013/01/30 18:02:48]

ViewHostMsg_UpdateFrameInfo is going to get deleted after
--enable-compositor-frame-message is set, so I recommend not doing this.  Just
leave them in separate values in the browser process calls and don't touch
UpdateFrameInfo in the renderer.

+  IPC_STRUCT_MEMBER(gfx::Vector2d, scroll_offset)
+  IPC_STRUCT_MEMBER(gfx::Vector2d, unused_scroll_delta)
+  IPC_STRUCT_MEMBER(float, page_scale_factor)
+  IPC_STRUCT_MEMBER(float, min_page_scale_factor)
+  IPC_STRUCT_MEMBER(float, max_page_scale_factor)
+  IPC_STRUCT_MEMBER(gfx::Size, content_size)
+IPC_STRUCT_END()
+
 // Messages sent from the browser to the renderer.
 
 // Set the top-level frame to the provided name.
@@ -1317,12 +1326,8 @@ IPC_MESSAGE_ROUTED1(ViewHostMsg_DidChangeBodyBackgroundColor,
 
 // Information about current document scroll, scale and size. Sent on a
 // best-effort basis.
-IPC_MESSAGE_ROUTED5(ViewHostMsg_UpdateFrameInfo,
-                    gfx::Vector2d /* scroll_offset */,
-                    float /* page_scale_factor */,
-                    float /* min_page_scale_factor */,
-                    float /* max_page_scale_factor */,
-                    gfx::Size /* content_size */)
+IPC_MESSAGE_ROUTED1(ViewHostMsg_UpdateFrameInfo,
+                    ViewHostMsg_UpdateFrameInfo_Params)
 
 #elif defined(OS_MACOSX)
 // Let the RenderView know its window has changed visibility.