Use DiscardableMemoryManager on Android.

base/memory/discardable_memory_allocator_android.h

-// Copyright 2013 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 BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
-#define BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_
-
-#include <string>
-
-#include "base/base_export.h"
-#include "base/basictypes.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/memory/scoped_vector.h"
-#include "base/synchronization/lock.h"
-#include "base/threading/thread_checker.h"
-
-namespace base {
-
-class DiscardableMemory;
-
-namespace internal {
-
-// On Android ashmem is used to implement discardable memory. It is backed by a
-// file (descriptor) thus is a limited resource. This allocator minimizes the
-// problem by allocating large ashmem regions internally and returning smaller
-// chunks to the client.
-// Allocated chunks are systematically aligned on a page boundary therefore this
-// allocator should not be used for small allocations.
-//
-// Threading: The allocator must be deleted on the thread it was constructed on
-// although its Allocate() method can be invoked on any thread. See
-// discardable_memory.h for DiscardableMemory's threading guarantees.
-class BASE_EXPORT_PRIVATE DiscardableMemoryAllocator {
- public:
-  // Note that |name| is only used for debugging/measurement purposes.
-  // |ashmem_region_size| is the size that will be used to create the underlying
-  // ashmem regions and is expected to be greater or equal than 32 MBytes.
-  DiscardableMemoryAllocator(const std::string& name,
-                             size_t ashmem_region_size);
-
-  ~DiscardableMemoryAllocator();
-
-  // Note that the allocator must outlive the returned DiscardableMemory
-  // instance.
-  scoped_ptr<DiscardableMemory> Allocate(size_t size);
-
-  // Returns the size of the last ashmem region which was created. This is used
-  // for testing only.
-  size_t last_ashmem_region_size() const;
-
- private:
-  class AshmemRegion;
-  class DiscardableAshmemChunk;
-
-  void DeleteAshmemRegion_Locked(AshmemRegion* region);
-
-  ThreadChecker thread_checker_;
-  const std::string name_;
-  const size_t ashmem_region_size_;
-  mutable Lock lock_;
-  size_t last_ashmem_region_size_;
-  ScopedVector<AshmemRegion> ashmem_regions_;
-
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAllocator);
-};
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATOR_H_