[WIP]Oilpan: checking for nearly-dead observers.

Source/platform/heap/Heap.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 858 matching lines @@
     // If a lazy sweep is in progress, returns true if the object was found
     // to be not reachable during the marking phase, but it has yet to be swept
     // and finalized. The predicate returns false in all other cases.
     //
     // Holding a reference to an already-dead object is not a valid state
     // to be in; willObjectBeLazilySwept() has undefined behavior if passed
     // such a reference.
     template<typename T>
     static bool willObjectBeLazilySwept(const T* objectPointer)
     {
+#if ENABLE(OILPAN)
+        // Restricted to Oilpan.
         static_assert(IsGarbageCollectedType<T>::value, "only objects deriving from GarbageCollected can be used.");
-#if ENABLE(OILPAN)
+#endif
         BasePage* page = pageFromObject(objectPointer);
         if (page->hasBeenSwept())
             return false;
         ASSERT(page->heap()->threadState()->isSweepingInProgress());
 
         return !ObjectAliveTrait<T>::isHeapObjectAlive(s_markingVisitor, const_cast<T*>(objectPointer));
-#else
-        // FIXME: remove when lazy sweeping is always on
-        // (cf. ThreadState::preSweep()).
-        return false;
-#endif
     }
 
     // Push a trace callback on the marking stack.
     static void pushTraceCallback(void* containerObject, TraceCallback);
 
     // Push a trace callback on the post-marking callback stack.  These
     // callbacks are called after normal marking (including ephemeron
     // iteration).
     static void pushPostMarkingCallback(void*, TraceCallback);
 
@@ skipping 383 matching lines @@
     size_t copySize = previousHeader->payloadSize();
     if (copySize > size)
         copySize = size;
     memcpy(address, previous, copySize);
     return address;
 }
 
 } // namespace blink
 
 #endif // Heap_h