ES6 symbols: Introduce Symbol class, along with abstract Name class

src/objects-printer.cc

Index: src/objects-printer.cc
diff --git a/src/objects-printer.cc b/src/objects-printer.cc
index 98868f29cb263efe61d4823ed30317049af157e8..ef030f0eff1e3d3654efcd05359e53c97b3b4f0e 100644
--- a/src/objects-printer.cc
+++ b/src/objects-printer.cc
@@ -76,6 +76,9 @@ void HeapObject::HeapObjectPrint(FILE* out) {
   }
 
   switch (instance_type) {
+    case SYMBOL_TYPE:
+      Symbol::cast(this)->SymbolPrint(out);
+      break;
     case MAP_TYPE:
       Map::cast(this)->MapPrint(out);
       break;
@@ -477,6 +480,7 @@ static const char* TypeToString(InstanceType type) {
     case INVALID_TYPE: return "INVALID";
     case MAP_TYPE: return "MAP";
     case HEAP_NUMBER_TYPE: return "HEAP_NUMBER";
+    case SYMBOL_TYPE: return "SYMBOL";
     case STRING_TYPE: return "TWO_BYTE_STRING";
     case ASCII_STRING_TYPE: return "ASCII_STRING";
     case CONS_STRING_TYPE: