src: add --track-heap-objects

- This makes v8 add .trace_function_info to the serialized form of
  snapshots from v8::HeapSnapshot::Serialize
- .trace_funciton_info combined with .trace_node in snapshots tells the
  JS location that allocated a specific object

PR-URL: https://github.com/nodejs/io.js/pull/2135
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

doc/iojs.1

@@ -60,6 +60,8 @@ and servers.
 
   --throw-deprecation    throw errors on deprecations
 
+  --track-heap-objects   track heap object allocations for heap snapshots
+
   --v8-options           print v8 command line options
 
 

src/node.cc

@@ -117,6 +117,7 @@ static bool trace_deprecation = false;
 static bool throw_deprecation = false;
 static bool abort_on_uncaught_exception = false;
 static bool trace_sync_io = false;
+static bool track_heap_objects = false;
 static const char* eval_string = nullptr;
 static unsigned int preload_module_count = 0;
 static const char** preload_modules = nullptr;
@@ -3065,6 +3066,8 @@ static void PrintHelp() {
          "  --trace-deprecation   show stack traces on deprecations\n"
          "  --trace-sync-io       show stack trace when use of sync IO\n"
          "                        is detected after the first tick\n"
+         "  --track-heap-objects  track heap object allocations for heap "
+         "snapshots\n"
          "  --v8-options          print v8 command line options\n"
 #if defined(NODE_HAVE_I18N_SUPPORT)
          "  --icu-data-dir=dir    set ICU data load path to dir\n"
@@ -3187,6 +3190,8 @@ static void ParseArgs(int* argc,
       trace_deprecation = true;
     } else if (strcmp(arg, "--trace-sync-io") == 0) {
       trace_sync_io = true;
+    } else if (strcmp(arg, "--track-heap-objects") == 0) {
+      track_heap_objects = true;
     } else if (strcmp(arg, "--throw-deprecation") == 0) {
       throw_deprecation = true;
     } else if (strcmp(arg, "--abort-on-uncaught-exception") == 0 ||
@@ -3876,6 +3881,10 @@ Environment* CreateEnvironment(Isolate* isolate,
 static void StartNodeInstance(void* arg) {
   NodeInstanceData* instance_data = static_cast<NodeInstanceData*>(arg);
   Isolate* isolate = Isolate::New();
+  if (track_heap_objects) {
+    isolate->GetHeapProfiler()->StartTrackingHeapObjects(true);
+  }
+
   // Fetch a reference to the main isolate, so we have a reference to it
   // even when we need it to access it from another (debugger) thread.
   if (instance_data->is_main())