[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..c5dcd4b7c77b1cf0c47ca4756c2b00ee4644cebb 100644
--- a/base/memory/discardable_shared_memory.cc
+++ b/base/memory/discardable_shared_memory.cc
@@ -340,6 +340,16 @@ bool DiscardableSharedMemory::IsMemoryResident() const {
          !result.GetTimestamp().is_null();
 }
 
+bool DiscardableSharedMemory::IsMemoryLocked() const {
+  if (!shared_memory_.memory())

[reveman, 2015/09/29 22:58:31]

nit: Can this be a DCHECK as IsMemoryResident?

[ssid, 2015/09/30 19:27:21]

Done.

+    return false;
+
+  SharedState result(subtle::NoBarrier_Load(
+      &SharedStateFromSharedMemory(shared_memory_)->value.i));
+
+  return result.GetLockState() == SharedState::LOCKED;
+}
+
 void DiscardableSharedMemory::Close() {
   shared_memory_.Close();
 }