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

base/memory/discardable_shared_memory.cc

Index: base/memory/discardable_shared_memory.cc
diff --git a/base/memory/discardable_shared_memory.cc b/base/memory/discardable_shared_memory.cc
index 0f85c1fe903d612ecf055043c1a0d84d362ddbf7..f36333a3500b6e2802dc454f110f1cb9ad143d71 100644
--- a/base/memory/discardable_shared_memory.cc
+++ b/base/memory/discardable_shared_memory.cc
@@ -340,6 +340,15 @@ bool DiscardableSharedMemory::IsMemoryResident() const {
          !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();
 }