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

base/memory/discardable_shared_memory.cc

 // 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.
 
 #include "base/memory/discardable_shared_memory.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
 #endif
 
@@ skipping 322 matching lines @@
 bool DiscardableSharedMemory::IsMemoryResident() const {
   DCHECK(shared_memory_.memory());
 
   SharedState result(subtle::NoBarrier_Load(
       &SharedStateFromSharedMemory(shared_memory_)->value.i));
 
   return result.GetLockState() == SharedState::LOCKED ||
          !result.GetTimestamp().is_null();
 }
 
+bool DiscardableSharedMemory::IsMemoryLocked() const {
+  DCHECK(IsMemoryResident());

[reveman, 2015/10/01 14:39:00]

hm, I was just thinking we'd DCHECK(shared_memory_.memory()) here. Why
DCHECK(IsMemoryResident())?

[ssid, 2015/10/01 14:48:24]

You told me to make it DCHECK(IsMemoryResident) in the previous comment. I think
it will be only called by host and for resident memory.

[reveman, 2015/10/01 14:54:13]

By "DCHECK as IsMemoryResident" I meant DCHECK in the same way
IsMemoryResident() does. Sorry for the confusion. I think
DCHECK(shared_memory_.memory()) is better here.

+
+  SharedState result(subtle::NoBarrier_Load(
+      &SharedStateFromSharedMemory(shared_memory_)->value.i));
+
+  return result.GetLockState() == SharedState::LOCKED;
+}
+
 void DiscardableSharedMemory::Close() {
   shared_memory_.Close();
 }
 
 #if defined(DISCARDABLE_SHARED_MEMORY_SHRINKING)
 void DiscardableSharedMemory::Shrink() {
 #if defined(OS_POSIX)
   SharedMemoryHandle handle = shared_memory_.handle();
   if (!SharedMemory::IsHandleValid(handle))
     return;
 
   // Truncate shared memory to size of SharedState.
   if (HANDLE_EINTR(ftruncate(SharedMemory::GetFdFromSharedMemoryHandle(handle),
                              AlignToPageSize(sizeof(SharedState)))) != 0) {
     DPLOG(ERROR) << "ftruncate() failed";
     return;
   }
   mapped_size_ = 0;
 #else
   NOTIMPLEMENTED();
 #endif
 }
 #endif
 
 Time DiscardableSharedMemory::Now() const {
   return Time::Now();
 }
 
 }  // namespace base