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

content/common/host_discardable_shared_memory_manager.cc

Index: content/common/host_discardable_shared_memory_manager.cc
diff --git a/content/common/host_discardable_shared_memory_manager.cc b/content/common/host_discardable_shared_memory_manager.cc
index 97351e5510538dd3fc1cbb6cdf0fbce27b5d5c0b..5858b63b0eb70e9120d0ac5140bfb2cd151d3774 100644
--- a/content/common/host_discardable_shared_memory_manager.cc
+++ b/content/common/host_discardable_shared_memory_manager.cc
@@ -180,9 +180,16 @@ bool HostDiscardableSharedMemoryManager::OnMemoryDump(
           "discardable/process_%x/segment_%d", child_process_id, segment_id);
       base::trace_event::MemoryAllocatorDump* dump =
           pmd->CreateAllocatorDump(dump_name);
+
+      const size_t mapped_size = segment->memory()->mapped_size();
       dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameSize,
                       base::trace_event::MemoryAllocatorDump::kUnitsBytes,
-                      segment->memory()->mapped_size());
+                      mapped_size);
+
+      // Host can only tell if whole segment is locked or not.
+      dump->AddScalar("locked_size",
+                      base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                      segment->memory()->IsMemoryLocked() ? mapped_size : 0u);
 
       // Create the cross-process ownership edge. If the child creates a
       // corresponding dump for the same segment, this will avoid to