[tracing] Fix the total size of V8 for debug mode

V8 makes resident all the memory it mmaps, filling it with 0xdeadbeef
for debug. But the dump provider only displays the live memory as
total, while it is supposed to display the resident size. This CL fixes
this to display correct resident size depending on the zapping.

BUG=546492

Review URL: https://codereview.chromium.org/1427513002

Cr-Commit-Position: refs/heads/master@{#357989}

1 files changed, 12 insertions, 0 deletions

diff --git a/gin/v8_isolate_memory_dump_provider.cc b/gin/v8_isolate_memory_dump_provider.cc
index 79c7177..55e6c50 100644
--- a/gin/v8_isolate_memory_dump_provider.cc
+++ b/gin/v8_isolate_memory_dump_provider.cc
@@ -103,6 +103,18 @@ void V8IsolateMemoryDumpProvider::DumpHeapStatistics(
                         base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                         heap_statistics.total_heap_size() - known_spaces_size);
 
+  // If V8 zaps garbage, all the memory mapped regions become resident,
+  // so we add an extra dump to avoid mismatches w.r.t. the total
+  // resident values.
+  if (heap_statistics.does_zap_garbage()) {
+    auto zap_dump = process_memory_dump->CreateAllocatorDump(
+        dump_base_name + "/zapped_for_debug");
+    zap_dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameSize,
+                        base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                        heap_statistics.total_heap_size() -
+                            heap_statistics.total_physical_size());
+  }
+
   // If light dump is requested, then object statistics are not dumped
   if (args.level_of_detail == base::trace_event::MemoryDumpLevelOfDetail::LIGHT)
     return;