Convert main-thread overscroll parameters into viewport space.

third_party/WebKit/public/web/WebWidgetClient.h

Index: third_party/WebKit/public/web/WebWidgetClient.h
diff --git a/third_party/WebKit/public/web/WebWidgetClient.h b/third_party/WebKit/public/web/WebWidgetClient.h
index 6497e9133e47621be7ba6d212929b2fb0cd5ac50..849a3d097d0a705b3bf16fe22638410d91fd4a9c 100644
--- a/third_party/WebKit/public/web/WebWidgetClient.h
+++ b/third_party/WebKit/public/web/WebWidgetClient.h
@@ -133,8 +133,13 @@ public:
     // Called when a gesture event is handled.
     virtual void didHandleGestureEvent(const WebGestureEvent& event, bool eventCancelled) { }
 
-    // Called when overscrolled on main thread.
-    virtual void didOverscroll(const WebFloatSize& unusedDelta, const WebFloatSize& accumulatedRootOverScroll, const WebFloatPoint& position, const WebFloatSize& velocity) { }
+    // Called when overscrolled on main thread. All parameters are in
+    // viewport-space.
+    virtual void didOverscroll(
+        const WebFloatSize& overscrollDelta,
+        const WebFloatSize& accumulatedOverscroll,
+        const WebFloatPoint& positionInViewport,
+        const WebFloatSize& velocityInViewport) { }
 
     // Called to update if touch events should be sent.
     virtual void hasTouchEventHandlers(bool) { }