[es2015] Precompute the descriptive string for symbols.

src/builtins/builtins-symbol.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/counters.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
 // -----------------------------------------------------------------------------
 // ES6 section 19.4 Symbol Objects
 
 // ES6 section 19.4.1.1 Symbol ( [ description ] ) for the [[Call]] case.
 BUILTIN(SymbolConstructor) {
   HandleScope scope(isolate);
-  Handle<Symbol> result = isolate->factory()->NewSymbol();
   Handle<Object> description = args.atOrUndefined(isolate, 1);
   if (!description->IsUndefined(isolate)) {
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, description,
                                        Object::ToString(isolate, description));
-    result->set_name(*description);
   }
-  return *result;
+  RETURN_RESULT_OR_FAILURE(isolate, isolate->factory()->NewSymbol(description));
 }
 
 // ES6 section 19.4.1.1 Symbol ( [ description ] ) for the [[Construct]] case.
 BUILTIN(SymbolConstructor_ConstructStub) {
   HandleScope scope(isolate);
   THROW_NEW_ERROR_RETURN_FAILURE(
       isolate, NewTypeError(MessageTemplate::kNotConstructor,
                             isolate->factory()->Symbol_string()));
 }
 
@@ skipping 24 matching lines @@
   } else {
     result = isolate->heap()->undefined_value();
   }
   DCHECK_EQ(isolate->heap()->public_symbol_table()->SlowReverseLookup(*symbol),
             result);
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8