Update from https://crrev.com/309717

base/memory/discardable_memory_shmem_allocator.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_SHMEM_ALLOCATOR_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_ALLOCATOR_H_
 
 #include "base/base_export.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
-class DiscardableSharedMemory;
+
+// TODO(reveman): Remove this by having allocator interface return
+// real DiscardableMemory instances. crbug.com/442945
+class BASE_EXPORT DiscardableMemoryShmemChunk {
+ public:
+  virtual ~DiscardableMemoryShmemChunk() {}
+
+  virtual bool Lock() = 0;
+  virtual void Unlock() = 0;
+  virtual void* Memory() const = 0;
+  virtual bool IsMemoryResident() const = 0;
+};
 
 class BASE_EXPORT DiscardableMemoryShmemAllocator {
  public:
   // Returns the allocator instance.
   static DiscardableMemoryShmemAllocator* GetInstance();
 
   // Sets the allocator instance. Can only be called once, e.g. on startup.
   // Ownership of |instance| remains with the caller.
   static void SetInstance(DiscardableMemoryShmemAllocator* allocator);
 
-  virtual scoped_ptr<DiscardableSharedMemory>
-  AllocateLockedDiscardableSharedMemory(size_t size) = 0;
+  virtual scoped_ptr<DiscardableMemoryShmemChunk>
+  AllocateLockedDiscardableMemory(size_t size) = 0;
 
  protected:
   virtual ~DiscardableMemoryShmemAllocator() {}
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_ALLOCATOR_H_