Whittle down some compositing chicken/egg hacks

Source/core/rendering/RenderLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 729 matching lines @@
 
     // FIXME: Need to detect a swap from custom to native scrollbars (and vice versa).
     if (m_hBar)
         m_hBar->styleChanged();
     if (m_vBar)
         m_vBar->styleChanged();
 
     updateScrollCornerStyle();
     updateResizerAreaSet();
     updateResizerStyle();
+
+    // FIXME: Remove incremental compositing updates after fixing the chicken/egg issues
+    // https://code.google.com/p/chromium/issues/detail?id=343756
+    DisableCompositingQueryAsserts disabler;
+    RenderLayer* layer = this->layer();
+    if (layer->hasCompositedLayerMapping() && layer->compositedLayerMapping()->updateGraphicsLayerConfiguration(GraphicsLayerUpdater::ForceUpdate))
+        layer->compositor()->setCompositingLayersNeedRebuild();
 }
 
 IntSize RenderLayerScrollableArea::clampScrollOffset(const IntSize& scrollOffset) const
 {
     int maxX = scrollWidth() - m_box->pixelSnappedClientWidth();
     int maxY = scrollHeight() - m_box->pixelSnappedClientHeight();
 
     int x = std::max(std::min(scrollOffset.width(), maxX), 0);
     int y = std::max(std::min(scrollOffset.height(), maxY), 0);
     return IntSize(x, y);
@@ skipping 785 matching lines @@
 void RenderLayerScrollableArea::setForceNeedsCompositedScrolling(ForceNeedsCompositedScrollingMode mode)
 {
     if (m_forceNeedsCompositedScrolling == mode)
         return;
 
     m_forceNeedsCompositedScrolling = mode;
     layer()->didUpdateNeedsCompositedScrolling();
 }
 
 } // Namespace WebCore