Fix event passing to overlay scrollbars when over a plugin

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 467 matching lines @@
     if (event.button == WebMouseEvent::ButtonLeft) {
         selectPopup = m_selectPopup;
         pagePopup = m_pagePopup;
         hidePopups();
         ASSERT(!m_selectPopup);
         ASSERT(!m_pagePopup);
     }
 
     m_lastMouseDownPoint = WebPoint(event.x, event.y);
 
-    if (event.button == WebMouseEvent::ButtonLeft) {
-        IntPoint point(event.x, event.y);
+    // Take capture on a mouse down on a plugin so we can send it mouse events.
+    // If the hit node is a plugin but a scrollbar is over it don't start mouse
+    // capture because it will interfere with the scrollbar receiving events.
+    IntPoint point(event.x, event.y);
+    if (event.button == WebMouseEvent::ButtonLeft && !m_page->mainFrame()->view()->scrollbarAtPoint(point)) {
         point = m_page->mainFrame()->view()->windowToContents(point);
         HitTestResult result(m_page->mainFrame()->eventHandler().hitTestResultAtPoint(point));
         Node* hitNode = result.innerNonSharedNode();
 
-        // Take capture on a mouse down on a plugin so we can send it mouse events.
-        if (hitNode && hitNode->renderer() && hitNode->renderer()->isEmbeddedObject()) {
+        if (!result.scrollbar() && hitNode && hitNode->renderer() && hitNode->renderer()->isEmbeddedObject()) {
             m_mouseCaptureNode = hitNode;
             TRACE_EVENT_ASYNC_BEGIN0("input", "capturing mouse", this);
         }
     }
 
     PageWidgetEventHandler::handleMouseDown(mainFrame, event);
 
     if (event.button == WebMouseEvent::ButtonLeft && m_mouseCaptureNode)
         m_mouseCaptureGestureToken = mainFrame.eventHandler().takeLastMouseDownGestureToken();
 
@@ skipping 3562 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