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

base/memory/discardable_memory_shmem_allocator.h

Index: base/memory/discardable_memory_shmem_allocator.h
diff --git a/base/memory/discardable_memory_shmem_allocator.h b/base/memory/discardable_memory_shmem_allocator.h
new file mode 100644
index 0000000000000000000000000000000000000000..68624b3960b3c979dd9989850361b93b12157f77
--- /dev/null
+++ b/base/memory/discardable_memory_shmem_allocator.h
@@ -0,0 +1,32 @@
+// 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;
+
+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;
+
+ protected:
+  virtual ~DiscardableMemoryShmemAllocator() {}
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_SHMEM_ALLOCATOR_H_