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

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index d4ebf651d764e4f85b3a8ddff28bc1a8617ee1c5..bb0f7442aef35a60fa6a26f99aebe98a0c6538f7 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -876,19 +876,16 @@ public:
     template<typename T>
     static bool willObjectBeLazilySwept(const T* objectPointer)
     {
-        static_assert(IsGarbageCollectedType<T>::value, "only objects deriving from GarbageCollected can be used.");
 #if ENABLE(OILPAN)
+        // Restricted to Oilpan.
+        static_assert(IsGarbageCollectedType<T>::value, "only objects deriving from GarbageCollected can be used.");
+#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.