Oilpan: like Vector<T>, restrict Deque<T> to certain part objects.

Source/wtf/Deque.h

Index: Source/wtf/Deque.h
diff --git a/Source/wtf/Deque.h b/Source/wtf/Deque.h
index 60eb8cfbe2c88d8f95231496efd8bcb717b580b8..ba354e23744677579254716fe65799271ef42808 100644
--- a/Source/wtf/Deque.h
+++ b/Source/wtf/Deque.h
@@ -226,6 +226,12 @@ namespace WTF {
         : m_start(0)
         , m_end(0)
     {
+        // Unused buffer slots are initialized to zero so that the visitor and the
+        // finalizer can visit them safely. canInitializeWithMemset tells us
+        // that the class does not expect matching constructor and
+        // destructor calls as long as the memory is zeroed.

[haraken, 2015/04/22 05:29:40]

Or can we add these static_assert to Vector::trace (or
HeapVectorBacking::trace)? Then we don't need to duplicate the static_asserts
between Vector and Deque.

[sof, 2015/04/22 16:05:21]

It makes some sense to keep it associated with the declaration of the collection
type, rather than where it is traced.

+        static_assert(!Allocator::isGarbageCollected || !VectorTraits<T>::needsDestruction || VectorTraits<T>::canInitializeWithMemset, "class has problems with finalizers called on cleared memory");
+        static_assert(!WTF::IsPolymorphic<T>::value || !VectorTraits<T>::canInitializeWithMemset, "cannot initialize with memset if there is a vtable");
     }
 
     template<typename T, size_t inlineCapacity, typename Allocator>