[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..aadda836ca290e6cd88b0c56794b32cad112420f 100644
--- a/content/common/host_discardable_shared_memory_manager.cc
+++ b/content/common/host_discardable_shared_memory_manager.cc
@@ -184,6 +184,11 @@ bool HostDiscardableSharedMemoryManager::OnMemoryDump(
                       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()->LockedSize());
+
       // 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