Make classes and structures in core/layout fast-allocated.

Source/core/layout/SubtreeLayoutScope.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef SubtreeLayoutScope_h
 #define SubtreeLayoutScope_h
 
 #include "core/inspector/InspectorTraceEvents.h"
+#include "wtf/Allocator.h"
 #include "wtf/HashSet.h"
 
 // This is the way to mark a subtree as needing layout during layout,
 // e.g. for the purposes of doing a multipass layout.
 //
 // It should only be used during layout. Outside of layout, you should
 // just call layoutObject->setNeedsLayout() directly.
 //
 // It ensures that you don't accidentally mark part of the tree as
 // needing layout and not actually lay it out.
 
 namespace blink {
 
 class LayoutObject;
 
 class SubtreeLayoutScope {
+    STACK_ALLOCATED();
 public:
     SubtreeLayoutScope(LayoutObject& root);
     ~SubtreeLayoutScope();
 
     void setNeedsLayout(LayoutObject* descendant, LayoutInvalidationReasonForTracing);
     void setChildNeedsLayout(LayoutObject* descendant);
 
     LayoutObject& root() { return m_root; }
     void recordObjectMarkedForLayout(LayoutObject*);
 
 private:
     LayoutObject& m_root;
 
 #if ENABLE(ASSERT)
     HashSet<LayoutObject*> m_layoutObjectsToLayout;
 #endif
 };
 
 }
 
 #endif