Correct alignment in ContiguousContainer::appendByMoving()

cc/base/contiguous_container.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 CC_BASE_CONTIGUOUS_CONTAINER_H_
 #define CC_BASE_CONTIGUOUS_CONTAINER_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 152 matching lines @@
   const BaseElementType& last() const { return *rbegin(); }
   BaseElementType& operator[](size_t index) { return *(begin() + index); }
   const BaseElementType& operator[](size_t index) const {
     return *(begin() + index);
   }
 
   template <class DerivedElementType, typename... Args>
   DerivedElementType& AllocateAndConstruct(Args&&... args) {
     static_assert(alignment % ALIGNOF(DerivedElementType) == 0,
                   "Derived type requires stronger alignment.");
-    size_t alloc_size = Align(sizeof(DerivedElementType));
-    return *new (Allocate(alloc_size))
+    return *new (AlignedAllocate(sizeof(DerivedElementType)))
         DerivedElementType(std::forward<Args>(args)...);
   }
 
   void RemoveLast() {
     DCHECK(!empty());
     last().~BaseElementType();
     ContiguousContainerBase::RemoveLast();
   }
 
   void Clear() {
     for (auto& element : *this) {
       // MSVC incorrectly reports this variable as unused.
       (void)element;
       element.~BaseElementType();
     }
     ContiguousContainerBase::Clear();
   }
 
   void Swap(ContiguousContainer& other) {
     ContiguousContainerBase::Swap(other);
   }
 
   // Appends a new element using memcpy, then default-constructs a base
   // element in its place. Use with care.
   BaseElementType& AppendByMoving(BaseElementType* item, size_t size) {
     DCHECK_GE(size, sizeof(BaseElementType));
-    void* new_item = Allocate(size);
+    void* new_item = AlignedAllocate(size);
     memcpy(new_item, static_cast<void*>(item), size);
     new (item) BaseElementType;
     return *static_cast<BaseElementType*>(new_item);
   }
 
  private:
-  static size_t Align(size_t size) {
+  void* AlignedAllocate(size_t size) {
+    void* result = ContiguousContainerBase::Allocate(Align(size));
+    DCHECK_EQ(reinterpret_cast<intptr_t>(result) & (alignment - 1), 0u);
+    return result;
+  }
+
+  size_t Align(size_t size) {
     size_t aligned_size = alignment * ((size + alignment - 1) / alignment);
     DCHECK_EQ(aligned_size % alignment, 0u);
     DCHECK_GE(aligned_size, size);
     DCHECK_LT(aligned_size, size + alignment);
     return aligned_size;
   }
 };
 
 }  // namespace cc
 
 #endif  // CC_BASE_CONTIGUOUS_CONTAINER_H_