Fix event passing to overlay scrollbars when over a plugin

Source/core/page/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 1269 matching lines @@
     if (mev.scrollbar()) {
         const bool wasLastScrollBar = mev.scrollbar() == m_lastScrollbarUnderMouse.get();
         HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::Active | HitTestRequest::ConfusingAndOftenMisusedDisallowShadowContent);
         mev = m_frame->document()->prepareMouseEvent(request, documentPoint, mouseEvent);
         if (wasLastScrollBar && mev.scrollbar() != m_lastScrollbarUnderMouse.get())
             m_lastScrollbarUnderMouse = nullptr;
     }
 
     if (swallowEvent) {
         // scrollbars should get events anyway, even disabled controls might be scrollable
-        Scrollbar* scrollbar = mev.scrollbar();
-
-        updateLastScrollbarUnderMouse(scrollbar, true);
-
-        if (scrollbar)
-            passMousePressEventToScrollbar(mev, scrollbar);
+        passMousePressEventToScrollbar(mev);
     } else {
         if (shouldRefetchEventTarget(mev)) {
             HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::Active | HitTestRequest::ConfusingAndOftenMisusedDisallowShadowContent);
             mev = m_frame->document()->prepareMouseEvent(request, documentPoint, mouseEvent);
         }
 
-        FrameView* view = m_frame->view();
-        Scrollbar* scrollbar = view ? view->scrollbarAtPoint(mouseEvent.position()) : 0;
-        if (!scrollbar)
-            scrollbar = mev.scrollbar();
-
-        updateLastScrollbarUnderMouse(scrollbar, true);
-
-        if (scrollbar && passMousePressEventToScrollbar(mev, scrollbar))
+        if (passMousePressEventToScrollbar(mev))
             swallowEvent = true;
         else
             swallowEvent = handleMousePressEvent(mev);
     }
 
     return swallowEvent;
 }
 
 static RenderLayer* layerForNode(Node* node)
 {
@@ skipping 1992 matching lines @@
         }
     }
 }
 
 void EventHandler::setFrameWasScrolledByUser()
 {
     if (FrameView* view = m_frame->view())
         view->setWasScrolledByUser(true);
 }
 
-bool EventHandler::passMousePressEventToScrollbar(MouseEventWithHitTestResults& mev, Scrollbar* scrollbar)
+bool EventHandler::passMousePressEventToScrollbar(MouseEventWithHitTestResults& mev)
 {
+    // First try to use the frame scrollbar.
+    FrameView* view = m_frame->view();
+    Scrollbar* scrollbar = view ? view->scrollbarAtPoint(mev.event().position()) : 0;
+
+    // Then try the scrollbar in the hit test.
+    if (!scrollbar)
+        scrollbar = mev.scrollbar();
+
+    updateLastScrollbarUnderMouse(scrollbar, true);
+
     if (!scrollbar || !scrollbar->enabled())
         return false;
     setFrameWasScrolledByUser();
     scrollbar->mouseDown(mev.event());
     return true;
 }
 
 // If scrollbar (under mouse) is different from last, send a mouse exited. Set
 // last to scrollbar if setLast is true; else set last to 0.
 void EventHandler::updateLastScrollbarUnderMouse(Scrollbar* scrollbar, bool setLast)
@@ skipping 399 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace WebCore