[es2015] Precompute the descriptive string for symbols.

src/runtime/runtime-symbol.cc

 // Copyright 2014 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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/isolate-inl.h"
 #include "src/objects-inl.h"
-#include "src/string-builder.h"
 
 namespace v8 {
 namespace internal {
 
 RUNTIME_FUNCTION(Runtime_CreateSymbol) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(Object, name, 0);
-  CHECK(name->IsString() || name->IsUndefined(isolate));
-  Handle<Symbol> symbol = isolate->factory()->NewSymbol();
-  if (name->IsString()) symbol->set_name(*name);
-  return *symbol;
+  RETURN_RESULT_OR_FAILURE(isolate, isolate->factory()->NewSymbol(name));
 }
 
-
 RUNTIME_FUNCTION(Runtime_CreatePrivateSymbol) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(Object, name, 0);
-  CHECK(name->IsString() || name->IsUndefined(isolate));
-  Handle<Symbol> symbol = isolate->factory()->NewPrivateSymbol();
-  if (name->IsString()) symbol->set_name(*name);
-  return *symbol;
+  RETURN_RESULT_OR_FAILURE(isolate, isolate->factory()->NewPrivateSymbol(name));
 }
 
-
 RUNTIME_FUNCTION(Runtime_SymbolDescription) {
   SealHandleScope shs(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_CHECKED(Symbol, symbol, 0);
   return symbol->name();
 }
 
-
 RUNTIME_FUNCTION(Runtime_SymbolDescriptiveString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(Symbol, symbol, 0);
-  IncrementalStringBuilder builder(isolate);
-  builder.AppendCString("Symbol(");
-  if (symbol->name()->IsString()) {
-    builder.AppendString(handle(String::cast(symbol->name()), isolate));
-  }
-  builder.AppendCharacter(')');
-  RETURN_RESULT_OR_FAILURE(isolate, builder.Finish());
+  return symbol->descriptive_string();
 }
 
-
 RUNTIME_FUNCTION(Runtime_SymbolIsPrivate) {
   SealHandleScope shs(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_CHECKED(Symbol, symbol, 0);
   return isolate->heap()->ToBoolean(symbol->is_private());
 }
+
 }  // namespace internal
 }  // namespace v8