Add support for ES6 Symbol in heap profiler

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index cafee77b4ce10d20be74ee3df7fe290349cff63f..d872e78a4fa2893c1b65d319abf6314e621d9283 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -155,6 +155,7 @@ const char* HeapEntry::TypeAsString() {
     case kSynthetic: return "/synthetic/";
     case kConsString: return "/concatenated string/";
     case kSlicedString: return "/sliced string/";
+    case kSymbol: return "/symbol/";
     default: return "???";
   }
 }
@@ -851,6 +852,8 @@ HeapEntry* V8HeapExplorer::AddEntry(HeapObject* object) {
     return AddEntry(object,
                     HeapEntry::kString,
                     names_->GetName(String::cast(object)));
+  } else if (object->IsSymbol()) {
+    return AddEntry(object, HeapEntry::kSymbol, "symbol");
   } else if (object->IsCode()) {
     return AddEntry(object, HeapEntry::kCode, "");
   } else if (object->IsSharedFunctionInfo()) {
@@ -1098,6 +1101,8 @@ bool V8HeapExplorer::ExtractReferencesPass1(int entry, HeapObject* obj) {
     ExtractJSObjectReferences(entry, JSObject::cast(obj));
   } else if (obj->IsString()) {
     ExtractStringReferences(entry, String::cast(obj));
+  } else if (obj->IsSymbol()) {
+    ExtractSymbolReferences(entry, Symbol::cast(obj));
   } else if (obj->IsMap()) {
     ExtractMapReferences(entry, Map::cast(obj));
   } else if (obj->IsSharedFunctionInfo()) {
@@ -1244,6 +1249,13 @@ void V8HeapExplorer::ExtractStringReferences(int entry, String* string) {
 }
 
 
+void V8HeapExplorer::ExtractSymbolReferences(int entry, Symbol* symbol) {
+  SetInternalReference(symbol, entry,
+                       "name", symbol->name(),
+                       Symbol::kNameOffset);
+}
+
+
 void V8HeapExplorer::ExtractContextReferences(int entry, Context* context) {
   if (context == context->declaration_context()) {
     ScopeInfo* scope_info = context->closure()->shared()->scope_info();