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..2b5cbaa1d12562f617f1e4d4b91532a7157d7605 100644
--- a/Source/core/frame/RootFrameViewport.cpp
+++ b/Source/core/frame/RootFrameViewport.cpp
@@ -96,9 +96,7 @@ ScrollResult RootFrameViewport::handleWheel(const PlatformWheelEvent& event)
 {
     updateScrollAnimator();
 
-    ScrollResult viewScrollResult;
-    if (layoutViewport().isScrollable())
-        viewScrollResult = layoutViewport().handleWheel(event);
+    ScrollResult viewScrollResult = layoutViewport().handleWheel(event);
 
     // The visual viewport will only accept pixel scrolls.
     if (!event.canScroll() || event.granularity() == ScrollByPageWheelEvent)
@@ -119,15 +117,10 @@ ScrollResult RootFrameViewport::handleWheel(const PlatformWheelEvent& event)
     DoublePoint targetPosition = visualViewport().adjustScrollPositionWithinRange(
         visualViewport().scrollPositionDouble() + toDoubleSize(locationDelta));
     visualViewport().setScrollPosition(targetPosition, UserScroll);
-
     DoublePoint usedLocationDelta(visualViewport().scrollPositionDouble() - oldOffset);
-    if (!viewScrollResult.didScroll() && usedLocationDelta == DoublePoint::zero())
-        return ScrollResult();
-
-    DoubleSize unusedLocationDelta(locationDelta - usedLocationDelta);
-    bool didScrollX = viewScrollResult.didScrollX || unusedLocationDelta.width();
-    bool didScrollY = viewScrollResult.didScrollY || unusedLocationDelta.height();
-    return ScrollResult(didScrollX, didScrollY, -unusedLocationDelta.width(), -unusedLocationDelta.height());
+    bool didScrollX = viewScrollResult.didScrollX || usedLocationDelta.x();
+    bool didScrollY = viewScrollResult.didScrollY || usedLocationDelta.y();
+    return ScrollResult(didScrollX, didScrollY, viewScrollResult.unusedScrollDeltaX - usedLocationDelta.x(), viewScrollResult.unusedScrollDeltaY - usedLocationDelta.y());

[bokan, 2015/06/25 17:50:31]

Is this working as expected? AFAICT, the unusedScrollDelta will be negative for
a downwards scroll but usedLocationDelta will be positive, so you'll get a
larger negative overscroll...

[MuVen, 2015/06/26 09:55:44]

You are right on this. i was negating the unusedDelta in the render_widget(which
i have noticed, on debugging, it was a mistake sorry:(). Changed as you have
suggested. Negating here itself. Will check the bug 504389 to ensure unusedDelta
state remains same everywhere. Thanks.

 }
 
 LayoutRect RootFrameViewport::scrollIntoView(const LayoutRect& rectInContent, const ScrollAlignment& alignX, const ScrollAlignment& alignY)