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

base/memory/discardable_memory.h

 // Copyright (c) 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_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_H_
 
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 
 enum DiscardableMemoryType {
   DISCARDABLE_MEMORY_TYPE_NONE,
   DISCARDABLE_MEMORY_TYPE_ASHMEM,
   DISCARDABLE_MEMORY_TYPE_MACH,
-  DISCARDABLE_MEMORY_TYPE_EMULATED
+  DISCARDABLE_MEMORY_TYPE_EMULATED,
+  DISCARDABLE_MEMORY_TYPE_SHMEM
 };
 
 enum DiscardableMemoryLockStatus {
   DISCARDABLE_MEMORY_LOCK_STATUS_FAILED,
   DISCARDABLE_MEMORY_LOCK_STATUS_PURGED,
   DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS
 };
 
 // Platform abstraction for discardable memory. DiscardableMemory is used to
 // cache large objects without worrying about blowing out memory, both on mobile
@@ skipping 48 matching lines @@
   // Gets the preferred discardable memory type.
   static DiscardableMemoryType GetPreferredType();
 
   // Create a DiscardableMemory instance with specified |type| and |size|.
   static scoped_ptr<DiscardableMemory> CreateLockedMemoryWithType(
       DiscardableMemoryType type, size_t size);
 
   // Create a DiscardableMemory instance with preferred type and |size|.
   static scoped_ptr<DiscardableMemory> CreateLockedMemory(size_t size);
 
+  // Discardable memory implementations might use this to release memory
+  // or resources assigned to instances that have been purged.
+  static void ReleaseFreeMemory();
+
   // Discardable memory implementations might allow an elevated usage level
   // while in frequent use. Call this to have the usage reduced to the base
   // level. Returns true if there's no need to call this again until
   // memory instances have been used. This indicates that all discardable
   // memory implementations have reduced usage to the base level or below.
   // Note: calling this too often or while discardable memory is in frequent
   // use can hurt performance, whereas calling it too infrequently can result
   // in memory bloat.
   static bool ReduceMemoryUsage();
 
@@ skipping 16 matching lines @@
   // Testing utility calls.
 
   // Purge all discardable memory in the system. This call has global effects
   // across all running processes, so it should only be used for testing!
   static void PurgeForTesting();
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_H_