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

content/common/discardable_shared_memory_heap.cc

Index: content/common/discardable_shared_memory_heap.cc
diff --git a/content/common/discardable_shared_memory_heap.cc b/content/common/discardable_shared_memory_heap.cc
index b641c0697442579e09a4b2801beca411f05540e3..c9c47d2883e6239a16b042175cd7a4bad86d8d93 100644
--- a/content/common/discardable_shared_memory_heap.cc
+++ b/content/common/discardable_shared_memory_heap.cc
@@ -395,6 +395,15 @@ void DiscardableSharedMemoryHeap::OnMemoryDump(
                           base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                           size);
 
+  ssize_t resident_size =
+      base::trace_event::ProcessMemoryDump::CountResidentBytes(
+          shared_memory->memory(), shared_memory->mapped_size());
+  if (resident_size >= 0) {
+    segment_dump->AddScalar("resident_size",
+                            base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                            static_cast<uint64>(resident_size));
+  }
+
   base::trace_event::MemoryAllocatorDump* obj_dump =
       pmd->CreateAllocatorDump(segment_dump_name + "/allocated_objects");
   obj_dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameObjectCount,