Reland of [tracing] Display the locked size of discardable memory segment.

base/memory/discardable_shared_memory.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_SHARED_MEMORY_H_
 #define BASE_MEMORY_DISCARDABLE_SHARED_MEMORY_H_
 
 #include "base/base_export.h"
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
@@ skipping 89 matching lines @@
   // purges the object using the updated |last_known_usage_|.
   // Note: there is no guarantee that multiple calls to this function will
   // successfully purge object. DiscardableSharedMemory object might be locked
   // or another thread/process might be able to lock and unlock it in between
   // each call.
   bool Purge(Time current_time);
 
   // Returns true if memory is still resident.
   bool IsMemoryResident() const;
 
+  // Returns true if memory is locked.
+  bool IsMemoryLocked() const;
+
   // Closes the open discardable memory segment.
   // It is safe to call Close repeatedly.
   void Close();
 
   // Shares the discardable memory segment to another process. Attempts to
   // create a platform-specific |new_handle| which can be used in a remote
   // process to access the discardable memory segment. |new_handle| is an
   // output parameter to receive the handle for use in the remote process.
   // Returns true on success, false otherwise.
   bool ShareToProcess(ProcessHandle process_handle,
@@ skipping 21 matching lines @@
   // synchronized somehow. Use a collision warner to detect incorrect usage.
   DFAKE_MUTEX(thread_collision_warner_);
   Time last_known_usage_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableSharedMemory);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_SHARED_MEMORY_H_