Separate the geometry update from rebuilding the GraphicsLayer tree

Source/platform/graphics/CompositingReasons.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CompositingReasons_h
 #define CompositingReasons_h
 
 #include "wtf/MathExtras.h"
 #include <stdint.h>
 
@@ skipping 99 matching lines @@
     | CompositingReasonIsolateCompositedDescendants
     | CompositingReasonPreserve3DWith3DDescendants; // preserve-3d has to create backing store to ensure that 3d-transformed elements intersect.
 
 const uint64_t CompositingReasonComboSquashableReasons =
     CompositingReasonOverlap
     | CompositingReasonAssumedOverlap
     | CompositingReasonOverflowScrollingParent;
 
 typedef uint64_t CompositingReasons;
 
+// Any reasons other than overlap or assumed overlap will require the layer to be separately compositing.
+inline bool requiresCompositing(CompositingReasons reasons)
+{
+    return reasons & ~CompositingReasonComboSquashableReasons;
+}
+
+// If the layer has overlap or assumed overlap, but no other reasons, then it should be squashed.
+inline bool requiresSquashing(CompositingReasons reasons)
+{
+    return !requiresCompositing(reasons) && (reasons & CompositingReasonComboSquashableReasons);
+}
+
 struct CompositingReasonStringMap {
     CompositingReasons reason;
     const char* shortName;
     const char* description;
 };
 
 // FIXME: This static data shouldn't be in a header. When it's in the header
 // it's copied into every compilation unit that includes the header.
 static const CompositingReasonStringMap compositingReasonStringMap[] = {
     { CompositingReasonNone,
@@ skipping 135 matching lines @@
         "layerForMask",
         "Secondary layer, to contain the mask contents" },
     { CompositingReasonLayerForClippingMask,
         "layerForClippingMask",
         "Secondary layer, for clipping mask" }
 };
 
 } // namespace WebCore
 
 #endif // CompositingReasons_h