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

base/memory/discardable_memory_manager.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_MANAGER_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_
 
 #include "base/base_export.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/mru_cache.h"
@@ skipping 13 matching lines @@
   virtual bool AllocateAndAcquireLock() = 0;
 
   // Release a previously acquired lock on the allocation so that it can be
   // purged by the system.
   virtual void ReleaseLock() = 0;
 
   // Explicitly purge this allocation. It is illegal to call this while a lock
   // is acquired on the allocation.
   virtual void Purge() = 0;
 
+  // Check if allocated memory is still resident. It is illegal to call this
+  // while a lock is acquired on the allocation.
+  virtual bool IsMemoryResident() const = 0;
+
  protected:
   virtual ~DiscardableMemoryManagerAllocation() {}
 };
 
 }  // namespace internal
 }  // namespace base
 
 namespace base {
 namespace internal {
 
@@ skipping 17 matching lines @@
   void SetMemoryLimit(size_t bytes);
 
   // The number of bytes of memory that may be allocated but unused for the hard
   // limit expiration time without getting purged.
   void SetSoftMemoryLimit(size_t bytes);
 
   // Sets the memory usage cutoff time for hard memory limit.
   void SetHardMemoryLimitExpirationTime(
       TimeDelta hard_memory_limit_expiration_time);
 
+  // This will make sure that all purged memory is released to the OS.
+  void ReleaseFreeMemory();
+
   // This will attempt to reduce memory footprint until within soft memory
   // limit. Returns true if there's no need to call this again until allocations
   // have been used.
   bool ReduceMemoryUsage();
 
   // This can be called to attempt to reduce memory footprint until within
   // limit for bytes to keep under moderate pressure.
   void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
 
   // Adds the given allocation to the manager's collection.
@@ skipping 76 matching lines @@
   // |soft_memory_limit_|.
   TimeDelta hard_memory_limit_expiration_time_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryManager);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_