[tracing] Display the resident size of the discardable memory segments

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 8af1d4dcc09912c2a6569fec88df88a33e54a0d7..a6d5e0739e96ff301b2582b1fee4f0cf16a92133 100644
--- a/content/common/host_discardable_shared_memory_manager.cc
+++ b/content/common/host_discardable_shared_memory_manager.cc
@@ -185,6 +185,15 @@ bool HostDiscardableSharedMemoryManager::OnMemoryDump(
                       base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                       segment->memory()->mapped_size());
 
+      ssize_t resident_size =
+          base::trace_event::ProcessMemoryDump::CountResidentBytes(
+              segment->memory()->memory(), segment->memory()->mapped_size());
+      if (resident_size >= 0) {
+        dump->AddScalar("resident_size",
+                        base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                        static_cast<uint64>(resident_size));
+      }
+
       // Host can only tell if whole segment is locked or not.
       dump->AddScalar(
           "locked_size", base::trace_event::MemoryAllocatorDump::kUnitsBytes,