Update from chromium https://crrev.com/301315

base/memory/discardable_memory_shmem.h

 // Copyright 2014 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_ASHMEM_H_
-#define BASE_MEMORY_DISCARDABLE_MEMORY_ASHMEM_H_
+#ifndef BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_H_
+#define BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_H_
 
 #include "base/memory/discardable_memory.h"
 
-#include "base/macros.h"
 #include "base/memory/discardable_memory_manager.h"
 
 namespace base {
+class DiscardableSharedMemory;
+
 namespace internal {
 
-class DiscardableAshmemChunk;
-class DiscardableMemoryAshmemAllocator;
-class DiscardableMemoryManager;
-
-class DiscardableMemoryAshmem
+class DiscardableMemoryShmem
     : public DiscardableMemory,
       public internal::DiscardableMemoryManagerAllocation {
  public:
-  explicit DiscardableMemoryAshmem(size_t bytes,
-                                   DiscardableMemoryAshmemAllocator* allocator,
-                                   DiscardableMemoryManager* manager);
+  explicit DiscardableMemoryShmem(size_t bytes);
+  virtual ~DiscardableMemoryShmem();
 
-  virtual ~DiscardableMemoryAshmem();
+  static void ReleaseFreeMemory();
+
+  static void PurgeForTesting();
 
   bool Initialize();
 
   // Overridden from DiscardableMemory:
   virtual DiscardableMemoryLockStatus Lock() override;
   virtual void Unlock() override;
   virtual void* Memory() const override;
 
   // Overridden from internal::DiscardableMemoryManagerAllocation:
   virtual bool AllocateAndAcquireLock() override;
   virtual void ReleaseLock() override;
   virtual void Purge() override;
+  virtual bool IsMemoryResident() const override;
 
  private:
   const size_t bytes_;
-  DiscardableMemoryAshmemAllocator* const allocator_;
-  DiscardableMemoryManager* const manager_;
+  scoped_ptr<DiscardableSharedMemory> shared_memory_;
   bool is_locked_;
-  scoped_ptr<DiscardableAshmemChunk> ashmem_chunk_;
 
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryAshmem);
+  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryShmem);
 };
 
 }  // namespace internal
 }  // namespace base
 
-#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_ASHMEM_H_
+#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_H_