Zero-initialize persistent heap vector inline backing buffers.

third_party/WebKit/Source/platform/heap/Handle.h

 /*
  * Copyright (C) 2014 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 608 matching lines @@
 
 template<
     typename ValueArg,
     typename HashFunctions = typename DefaultHash<ValueArg>::Hash,
     typename Traits = HashTraits<ValueArg>>
 class PersistentHeapHashCountedSet : public PersistentHeapCollectionBase<HeapHashCountedSet<ValueArg, HashFunctions, Traits>> { };
 
 template<typename T, size_t inlineCapacity = 0>
 class PersistentHeapVector : public PersistentHeapCollectionBase<HeapVector<T, inlineCapacity>> {
 public:
-    PersistentHeapVector() { }
+    PersistentHeapVector()
+    {
+        initializeUnusedSlots();
+    }
 
     explicit PersistentHeapVector(size_t size)
         : PersistentHeapCollectionBase<HeapVector<T, inlineCapacity>>(size)
     {
+        initializeUnusedSlots();
+    }
+
+    PersistentHeapVector(const PersistentHeapVector& other)
+        : PersistentHeapCollectionBase<HeapVector<T, inlineCapacity>>(other)
+    {
+        initializeUnusedSlots();
     }
 
     template<size_t otherCapacity>
     PersistentHeapVector(const HeapVector<T, otherCapacity>& other)
         : PersistentHeapCollectionBase<HeapVector<T, inlineCapacity>>(other)
     {
+        initializeUnusedSlots();
+    }
+
+private:
+    void initializeUnusedSlots()
+    {
+        // The PersistentHeapVector is allocated off heap along with its
+        // inline buffer (if any.) Maintain the invariant that unused
+        // slots are cleared for the off-heap inline buffer also.
+        size_t unusedSlots = this->capacity() - this->size();
+        if (unusedSlots)
+            this->clearUnusedSlots(this->end(), this->end() + unusedSlots);
     }
 };
 
 template<typename T, size_t inlineCapacity = 0>
 class PersistentHeapDeque : public PersistentHeapCollectionBase<HeapDeque<T, inlineCapacity>> {
 public:
     PersistentHeapDeque() { }
 
     template<size_t otherCapacity>
     PersistentHeapDeque(const HeapDeque<T, otherCapacity>& other)
@@ skipping 846 matching lines @@
     // TODO(sof): extend WTF::FunctionWrapper call overloading to also handle (CrossThread)WeakPersistent.
     static T* unwrap(const StorageType& value) { return value.get(); }
 };
 
 template<typename T>
 PassRefPtr<T> adoptRef(blink::RefCountedGarbageCollected<T>*) = delete;
 
 } // namespace WTF
 
 #endif