base: Add soft memory limit to DiscardableMemoryManager.

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>
 
@@ skipping 79 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);
 
+  // Call this when idle. Discardable memory implementations might use this
+  // to reduce memory footprint. 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 done as much cleanup as they
+  // will be able to do.
+  static bool IdleNotification();
+
   // Locks the memory so that it will not be purged by the system. Returns
   // DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS on success. If the return value is
   // DISCARDABLE_MEMORY_LOCK_STATUS_FAILED then this object should be
   // discarded and a new one should be created. If the return value is
   // DISCARDABLE_MEMORY_LOCK_STATUS_PURGED then the memory is present but any
   // data that was in it is gone.
   virtual DiscardableMemoryLockStatus Lock() WARN_UNUSED_RESULT = 0;
 
   // Unlocks the memory so that it can be purged by the system. Must be called
   // after every successful lock call.
   virtual void Unlock() = 0;
 
   // Returns the memory address held by this object. The object must be locked
   // before calling this. Otherwise, this will cause a DCHECK error.
   virtual void* Memory() const = 0;
 
   // 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_