Report accurate Overscroll on handleWheel.

Source/core/frame/RootFrameViewport.cpp

Index: Source/core/frame/RootFrameViewport.cpp
diff --git a/Source/core/frame/RootFrameViewport.cpp b/Source/core/frame/RootFrameViewport.cpp
index 3ba978fd47f6bf304fb7f05ff327a2e0d915b761..e3a33ff359e6dab14f1de2fae4f6973cbf83a4f7 100644
--- a/Source/core/frame/RootFrameViewport.cpp
+++ b/Source/core/frame/RootFrameViewport.cpp
@@ -122,7 +122,7 @@ ScrollResult RootFrameViewport::handleWheel(const PlatformWheelEvent& event)
 
     DoublePoint usedLocationDelta(visualViewport().scrollPositionDouble() - oldOffset);
     if (!viewScrollResult.didScroll() && usedLocationDelta == DoublePoint::zero())
-        return ScrollResult();
+        return ScrollResult(false, false, viewScrollResult.unusedScrollDeltaX, viewScrollResult.unusedScrollDeltaY);

[bokan, 2015/06/23 16:20:45]

This is returning the layout viewport's overscroll, which can be consumed by the
visual viewport. You need to subtract out the usedLocationDelta (how much the
visual viewport scrolled)

[MuVen, 2015/06/25 12:55:51]

Done.

 
     DoubleSize unusedLocationDelta(locationDelta - usedLocationDelta);
     bool didScrollX = viewScrollResult.didScrollX || unusedLocationDelta.width();