[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..8af1d4dcc09912c2a6569fec88df88a33e54a0d7 100644
--- a/content/common/host_discardable_shared_memory_manager.cc
+++ b/content/common/host_discardable_shared_memory_manager.cc
@@ -180,10 +180,17 @@ bool HostDiscardableSharedMemoryManager::OnMemoryDump(
           "discardable/process_%x/segment_%d", child_process_id, segment_id);
       base::trace_event::MemoryAllocatorDump* dump =
           pmd->CreateAllocatorDump(dump_name);
+
       dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameSize,
                       base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                       segment->memory()->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() ? segment->memory()->mapped_size()
+                                              : 0u);
+
       // Create the cross-process ownership edge. If the child creates a
       // corresponding dump for the same segment, this will avoid to
       // double-count them in tracing. If, instead, no other process will emit a