Plumb CompositingReason from Blink to compositor.

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 73 matching lines @@
     CompositingReasonNone                                   = 0,
 
     // Intrinsic reasons that can be known right away by the layer
     CompositingReason3DTransform                            = 1 << 0,
     CompositingReasonVideo                                  = 1 << 1,
     CompositingReasonCanvas                                 = 1 << 2,
     CompositingReasonPlugin                                 = 1 << 3,
     CompositingReasonIFrame                                 = 1 << 4,
     CompositingReasonBackfaceVisibilityHidden               = 1 << 5,
     CompositingReasonAnimation                              = 1 << 6,
-    CompositingReasonTransition                             = 1 << 7,
-    CompositingReasonFilters                                = 1 << 8,
-    CompositingReasonPositionFixed                          = 1 << 9,
-    CompositingReasonPositionSticky                         = 1 << 10,
-    CompositingReasonOverflowScrollingTouch                 = 1 << 11,
-    CompositingReasonBlending                               = 1 << 12,
+    CompositingReasonFilters                                = 1 << 7,
+    CompositingReasonPositionFixed                          = 1 << 8,
+    CompositingReasonPositionSticky                         = 1 << 9,
+    CompositingReasonOverflowScrollingTouch                 = 1 << 10,
+    CompositingReasonBlending                               = 1 << 11,
 
     // Overlap reasons that require knowing what's behind you in paint-order before knowing the answer
-    CompositingReasonAssumedOverlap                         = 1 << 13,
-    CompositingReasonOverlap                                = 1 << 14,
-    CompositingReasonNegativeZIndexChildren                 = 1 << 15,
+    CompositingReasonAssumedOverlap                         = 1 << 12,
+    CompositingReasonOverlap                                = 1 << 13,
+    CompositingReasonNegativeZIndexChildren                 = 1 << 14,
 
     // Subtree reasons that require knowing what the status of your subtree is before knowing the answer
-    CompositingReasonTransformWithCompositedDescendants     = 1 << 16,
-    CompositingReasonOpacityWithCompositedDescendants       = 1 << 17,
-    CompositingReasonMaskWithCompositedDescendants          = 1 << 18,
-    CompositingReasonReflectionWithCompositedDescendants    = 1 << 19,
-    CompositingReasonFilterWithCompositedDescendants        = 1 << 20,
-    CompositingReasonBlendingWithCompositedDescendants      = 1 << 21,
-    CompositingReasonClipsCompositingDescendants            = 1 << 22,
-    CompositingReasonPerspective                            = 1 << 23,
-    CompositingReasonPreserve3D                             = 1 << 24,
-    CompositingReasonReflectionOfCompositedParent           = 1 << 25,
+    CompositingReasonTransformWithCompositedDescendants     = 1 << 15,
+    CompositingReasonOpacityWithCompositedDescendants       = 1 << 16,
+    CompositingReasonMaskWithCompositedDescendants          = 1 << 17,
+    CompositingReasonReflectionWithCompositedDescendants    = 1 << 18,
+    CompositingReasonFilterWithCompositedDescendants        = 1 << 19,
+    CompositingReasonBlendingWithCompositedDescendants      = 1 << 20,
+    CompositingReasonClipsCompositingDescendants            = 1 << 21,
+    CompositingReasonPerspective                            = 1 << 22,
+    CompositingReasonPreserve3D                             = 1 << 23,
+    CompositingReasonReflectionOfCompositedParent           = 1 << 24,
 
     // The root layer is a special case that may be forced to be a layer, but also it needs to be
     // a layer if anything else in the subtree is composited.
-    CompositingReasonRoot                                   = 1 << 26
+    CompositingReasonRoot                                   = 1 << 25,
+
+    // RenderLayerBacking internal hierarchy reasons
+    CompositingReasonLayerForClip                           = 1 << 26,
+    CompositingReasonLayerForScrollbar                      = 1 << 27,
+    CompositingReasonLayerForScrollingContainer             = 1 << 28,
+    CompositingReasonLayerForForeground                     = 1 << 29,
+    CompositingReasonLayerForBackground                     = 1 << 30,
+    CompositingReasonLayerForMask                           = 1 << 31,
+
+    // Note: if you add more reasons here, you will need to update the WebCompositingReasons enum as well.
 };
 typedef unsigned CompositingReasons;
 
 class ClipRect {
 public:
     ClipRect()
     : m_hasRadius(false)
     { }
     
     ClipRect(const LayoutRect& rect)
@@ skipping 1210 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