[runtime] Rewrite Function.prototype.toString in C++.

src/js/messages.js

Index: src/js/messages.js
diff --git a/src/js/messages.js b/src/js/messages.js
index 8016c4d5ee8ed5354330f6525779a5d6d90d6c00..6b7306a7d35c6c54190c420b0a9804034edd3692 100644
--- a/src/js/messages.js
+++ b/src/js/messages.js
@@ -27,7 +27,6 @@ var FLAG_harmony_tostring;
 var Float32x4ToString;
 var formattedStackTraceSymbol =
     utils.ImportNow("formatted_stack_trace_symbol");
-var FunctionSourceString
 var GlobalObject = global.Object;
 var Int16x8ToString;
 var Int32x4ToString;
@@ -53,7 +52,6 @@ utils.Import(function(from) {
   Bool32x4ToString = from.Bool32x4ToString;
   Bool8x16ToString = from.Bool8x16ToString;
   Float32x4ToString = from.Float32x4ToString;
-  FunctionSourceString = from.FunctionSourceString;
   Int16x8ToString = from.Int16x8ToString;
   Int32x4ToString = from.Int32x4ToString;
   Int8x16ToString = from.Int8x16ToString;
@@ -120,7 +118,7 @@ function NoSideEffectsToString(obj) {
   if (IS_UNDEFINED(obj)) return 'undefined';
   if (IS_NULL(obj)) return 'null';
   if (IS_FUNCTION(obj)) {
-    var str = %_Call(FunctionSourceString, obj, obj);
+    var str = %FunctionToString(obj);
     if (str.length > 128) {
       str = %_SubString(str, 0, 111) + "...<omitted>..." +
             %_SubString(str, str.length - 2, str.length);