[builtins] Unify the String constructor.

src/runtime/runtime-symbol.cc

Index: src/runtime/runtime-symbol.cc
diff --git a/src/runtime/runtime-symbol.cc b/src/runtime/runtime-symbol.cc
index 03bd76ce27f9eff9dc75872acd7c22e9aedee793..778c2417095ba7ed96c272dc8ffa7f16eea1f53a 100644
--- a/src/runtime/runtime-symbol.cc
+++ b/src/runtime/runtime-symbol.cc
@@ -5,7 +5,9 @@
 #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 {
@@ -38,6 +40,22 @@ RUNTIME_FUNCTION(Runtime_SymbolDescription) {
 }
 
 
+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(')');
+  Handle<String> result;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result, builder.Finish());
+  return *result;
+}
+
+
 RUNTIME_FUNCTION(Runtime_SymbolRegistry) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 0);