Reset unusedDelta on Onverscroll for residual values.

Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 114 matching lines @@
 // The minimum amount of time an element stays active after a ShowPress
 // This is roughly 9 frames, which should be long enough to be noticeable.
 static const double minimumActiveInterval = 0.15;
 
 #if OS(MACOSX)
 static const double TextDragDelay = 0.15;
 #else
 static const double TextDragDelay = 0.0;
 #endif
 
+// Report Overscroll if OverscrollDelta is greater than minimumOverscrollDelta
+// to maintain consistency as did in compositor.
+static const float minimumOverscrollDelta = 0.1;
+
 enum NoCursorChangeType { NoCursorChange };
 
 enum class DragInitiator { Mouse, Touch };
 
 class OptionalCursor {
 public:
     OptionalCursor(NoCursorChangeType) : m_isCursorChange(false) { }
     OptionalCursor(const Cursor& cursor) : m_isCursorChange(true), m_cursor(cursor) { }
 
     bool isCursorChange() const { return m_isCursorChange; }
@@ skipping 2089 matching lines @@
 }
 
 void EventHandler::resetOverscroll(bool didScrollX, bool didScrollY)
 {
     if (didScrollX)
         m_accumulatedRootOverscroll.setWidth(0);
     if (didScrollY)
         m_accumulatedRootOverscroll.setHeight(0);
 }
 
+static inline FloatSize adjustOverscoll(FloatSize unusedDelta)
+{
+    if (std::abs(unusedDelta.width()) < minimumOverscrollDelta)
+        unusedDelta.setWidth(0);
+    if (std::abs(unusedDelta.height()) < minimumOverscrollDelta)
+        unusedDelta.setHeight(0);
+
+    return unusedDelta;
+}
+
 void EventHandler::handleOverscroll(const ScrollResult& scrollResult, const FloatPoint& position, const FloatSize& velocity)
 {
     FloatSize unusedDelta(scrollResult.unusedScrollDeltaX, scrollResult.unusedScrollDeltaY);
+    unusedDelta = adjustOverscoll(unusedDelta);
     resetOverscroll(scrollResult.didScrollX, scrollResult.didScrollY);
     if (unusedDelta != FloatSize()) {
         m_accumulatedRootOverscroll += unusedDelta;
         m_frame->chromeClient().didOverscroll(unusedDelta, m_accumulatedRootOverscroll, position, velocity);
     }
 }
 
 bool EventHandler::handleGestureScrollUpdate(const PlatformGestureEvent& gestureEvent)
 {
     ASSERT(gestureEvent.type() == PlatformEvent::GestureScrollUpdate);
@@ skipping 1666 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace blink