New UMA stats for stacking container opt-in measurements.

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 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 1107 matching lines @@
 
     // This is true if we have an out-of-flow positioned descendant whose
     // containing block is our ancestor. If this is the case, the descendant
     // may fall outside of our clip preventing things like opting into
     // composited scrolling (which causes clipping of all descendants).
     unsigned m_hasUnclippedDescendant : 1;
 
     unsigned m_isUnclippedDescendant : 1;
 
     unsigned m_needsCompositedScrolling : 1;
+    unsigned m_needsCompositedScrollingHasBeenRecorded : 1;
+    unsigned m_willUseCompositedScrollingHasBeenRecorded : 1;
+
+    unsigned m_isScrollableAreaHasBeenRecorded : 1;
 
     // If this is true, then no non-descendant appears between any of our
     // descendants in stacking order. This is one of the requirements of being
     // able to safely become a stacking context.
     unsigned m_canBePromotedToStackingContainer : 1;
     unsigned m_canBePromotedToStackingContainerDirty : 1;
 
     const unsigned m_isRootLayer : 1;
 
     unsigned m_usedTransparency : 1; // Tracks whether we need to close a transparent layer, i.e., whether
@@ skipping 160 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h