Force layout for main thread scrolling.

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 922 matching lines @@
 
     if (!node)
         node = m_frame->document()->focusedElement();
 
     if (!node)
         node = m_mousePressNode.get();
 
     if (!node || !node->layoutObject())
         return false;
 
+    m_frame->document()->updateLayoutIgnorePendingStylesheets();
+
     LayoutBox* curBox = node->layoutObject()->enclosingBox();
     while (curBox && !curBox->isLayoutView()) {
         ScrollDirectionPhysical physicalDirection = toPhysicalDirection(
             direction, curBox->isHorizontalWritingMode(), curBox->style()->isFlippedBlocksWritingMode());
 
         // If we're at the stopNode, we should try to scroll it but we shouldn't bubble past it
         bool shouldStopBubbling = stopNode && *stopNode && curBox->node() == *stopNode;
         bool didScroll = curBox->scroll(physicalDirection, granularity, delta);
 
         if (didScroll && stopNode)
@@ skipping 3219 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace blink