Update from https://crrev.com/320343

base/memory/discardable_memory_emulated.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_EMULATED_H_
-#define BASE_MEMORY_DISCARDABLE_MEMORY_EMULATED_H_
-
-#include "base/memory/discardable_memory.h"
-
-#include "base/memory/discardable_memory_manager.h"
-
-namespace base {
-namespace internal {
-
-class DiscardableMemoryEmulated
-    : public DiscardableMemory,
-      public internal::DiscardableMemoryManagerAllocation {
- public:
-  explicit DiscardableMemoryEmulated(size_t bytes);
-  ~DiscardableMemoryEmulated() override;
-
-  static bool ReduceMemoryUsage();
-
-  // TODO(reveman): Remove this as it is breaking the discardable memory design
-  // principle that implementations should not rely on information this is
-  // unavailable in kernel space. crbug.com/400423
-  BASE_EXPORT static void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
-
-  bool Initialize();
-
-  // Overridden from DiscardableMemory:
-  DiscardableMemoryLockStatus Lock() override;
-  void Unlock() override;
-  void* Memory() const override;
-
-  // Overridden from internal::DiscardableMemoryManagerAllocation:
-  bool AllocateAndAcquireLock() override;
-  void ReleaseLock() override {}
-  void Purge() override;
-
- private:
-  const size_t bytes_;
-  scoped_ptr<uint8[]> memory_;
-  bool is_locked_;
-
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryEmulated);
-};
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_EMULATED_H_