Enable per thread heap for database thread

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef HeapAllocator_h
 #define HeapAllocator_h
 
 #include "platform/heap/Heap.h"
 #include "platform/heap/TraceTraits.h"
 #include "wtf/Allocator.h"
@@ skipping 554 matching lines @@
 template<typename T, size_t inlineCapacity>
 struct NeedsTracing<ListHashSetNode<T, blink::HeapListHashSetAllocator<T, inlineCapacity>> *> {
     STATIC_ONLY(NeedsTracing);
     static_assert(sizeof(T), "T must be fully defined");
     // All heap allocated node pointers need visiting to keep the nodes alive,
     // regardless of whether they contain pointers to other heap allocated
     // objects.
     static const bool value = true;
 };
 
+template<typename T> struct HashTraits<blink::CrossThreadPersistent<T>> : SimpleClassHashTraits<blink::CrossThreadPersistent<T>> {
+    STATIC_ONLY(HashTraits);
+    // FIXME: The distinction between PeekInType and PassInType is there for
+    // the sake of the reference counting handles. When they are gone the two
+    // types can be merged into PassInType.
+    // FIXME: Implement proper const'ness for iterator types. Requires support
+    // in the marking Visitor.
+    using PeekInType = T*;
+    using PassInType = T*;
+    using IteratorGetType = blink::Member<T>*;
+    using IteratorConstGetType = const blink::CrossThreadPersistent<T>*;
+    using IteratorReferenceType = blink::CrossThreadPersistent<T>&;
+    using IteratorConstReferenceType = const blink::CrossThreadPersistent<T>&;
+    static IteratorReferenceType getToReferenceConversion(IteratorGetType x) { return *x; }
+    static IteratorConstReferenceType getToReferenceConstConversion(IteratorConstGetType x) { return *x; }
+    // FIXME: Similarly, there is no need for a distinction between PeekOutType
+    // and PassOutType without reference counting.
+    using PeekOutType = T*;
+    using PassOutType = T*;
+
+    template<typename U>
+    static void store(const U& value, blink::CrossThreadPersistent<T>& storage) { storage = value; }
+
+    static PeekOutType peek(const blink::CrossThreadPersistent<T>& value) { return value; }
+    static PassOutType passOut(const blink::CrossThreadPersistent<T>& value) { return value; }
+};
+
 } // namespace WTF
 
 #endif