Early terminate flings when scrolling impossible

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 539 matching lines @@
         mouseContextMenu(event);
 #endif
 }
 
 bool WebViewImpl::handleMouseWheel(LocalFrame& mainFrame, const WebMouseWheelEvent& event)
 {
     hidePopups();
     return PageWidgetEventHandler::handleMouseWheel(mainFrame, event);
 }
 
-void WebViewImpl::scrollBy(const WebFloatSize& delta)
+bool WebViewImpl::scrollBy(const WebFloatSize& delta, const WebFloatSize& velocity)
 {
     if (m_flingSourceDevice == WebGestureEvent::Touchpad) {
         WebMouseWheelEvent syntheticWheel;
         const float tickDivisor = WebCore::WheelEvent::TickMultiplier;
 
         syntheticWheel.deltaX = delta.width;
         syntheticWheel.deltaY = delta.height;
         syntheticWheel.wheelTicksX = delta.width / tickDivisor;
         syntheticWheel.wheelTicksY = delta.height / tickDivisor;
         syntheticWheel.hasPreciseScrollingDeltas = true;
         syntheticWheel.x = m_positionOnFlingStart.x;
         syntheticWheel.y = m_positionOnFlingStart.y;
         syntheticWheel.globalX = m_globalPositionOnFlingStart.x;
         syntheticWheel.globalY = m_globalPositionOnFlingStart.y;
         syntheticWheel.modifiers = m_flingModifier;
 
         if (m_page && m_page->mainFrame() && m_page->mainFrame()->view())
-            handleMouseWheel(*m_page->mainFrame(), syntheticWheel);
+            return handleMouseWheel(*m_page->mainFrame(), syntheticWheel);
     } else {
         WebGestureEvent syntheticGestureEvent;
 
         syntheticGestureEvent.type = WebInputEvent::GestureScrollUpdateWithoutPropagation;
         syntheticGestureEvent.data.scrollUpdate.deltaX = delta.width;
         syntheticGestureEvent.data.scrollUpdate.deltaY = delta.height;
         syntheticGestureEvent.x = m_positionOnFlingStart.x;
         syntheticGestureEvent.y = m_positionOnFlingStart.y;
         syntheticGestureEvent.globalX = m_globalPositionOnFlingStart.x;
         syntheticGestureEvent.globalY = m_globalPositionOnFlingStart.y;
         syntheticGestureEvent.modifiers = m_flingModifier;
         syntheticGestureEvent.sourceDevice = WebGestureEvent::Touchscreen;
 
         if (m_page && m_page->mainFrame() && m_page->mainFrame()->view())
-            handleGestureEvent(syntheticGestureEvent);
+            return handleGestureEvent(syntheticGestureEvent);
     }
+    return false;
+}
+
+void WebViewImpl::scrollBy(const WebFloatSize& delta)
+{
+    scrollBy(delta, WebFloatSize());
 }
 
 bool WebViewImpl::handleGestureEvent(const WebGestureEvent& event)
 {
     bool eventSwallowed = false;
     bool eventCancelled = false; // for disambiguation
 
     // Special handling for slow-path fling gestures.
     switch (event.type) {
     case WebInputEvent::GestureFlingStart: {
@@ skipping 3398 matching lines @@
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     if (!mainFrameImpl() || !mainFrameImpl()->frameView())
         return false;
 
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace blink