Lock the prototype of internal classes.

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index a70eeade83b9d68b51937611b621b628fa6be286..6f68ce089096db33a4e5c3f52a9a4ead7595400c 100644
--- a/src/string.js
+++ b/src/string.js
@@ -911,50 +911,47 @@ function ReplaceResultBuilder(str) {
   this.special_string = str;
 }
 
-ReplaceResultBuilder.prototype.__proto__ = null;
-
-
-ReplaceResultBuilder.prototype.add = function(str) {
-  str = TO_STRING_INLINE(str);
-  if (str.length > 0) this.elements.push(str);
-}
-
-
-ReplaceResultBuilder.prototype.addSpecialSlice = function(start, end) {
-  var len = end - start;
-  if (start < 0 || len <= 0) return;
-  if (start < 0x80000 && len < 0x800) {
-    this.elements.push((start << 11) | len);
-  } else {
-    // 0 < len <= String::kMaxLength and Smi::kMaxValue >= String::kMaxLength,
-    // so -len is a smi.
+SetUpLockedPrototype(ReplaceResultBuilder,
+  $Array("elements", "special_string"), $Array(
+  "add", function(str) {
+    str = TO_STRING_INLINE(str);
+    if (str.length > 0) this.elements.push(str);
+  },
+  "addSpecialSlice", function(start, end) {
+    var len = end - start;
+    if (start < 0 || len <= 0) return;
+    if (start < 0x80000 && len < 0x800) {
+      this.elements.push((start << 11) | len);
+    } else {
+      // 0 < len <= String::kMaxLength and Smi::kMaxValue >= String::kMaxLength,
+      // so -len is a smi.
+      var elements = this.elements;
+      elements.push(-len);
+      elements.push(start);
+    }
+  },
+  "generate", function() {
     var elements = this.elements;
-    elements.push(-len);
-    elements.push(start);
+    return %StringBuilderConcat(elements, elements.length, this.special_string);
   }
-}
-
-
-ReplaceResultBuilder.prototype.generate = function() {
-  var elements = this.elements;
-  return %StringBuilderConcat(elements, elements.length, this.special_string);
-}
+));
 
 
 // -------------------------------------------------------------------
 
-function SetupString() {
-  // Setup the constructor property on the String prototype object.
+function SetUpString() {
+  %CheckIsBootstrapping();
+  // Set up the constructor property on the String prototype object.
   %SetProperty($String.prototype, "constructor", $String, DONT_ENUM);
 
 
-  // Setup the non-enumerable functions on the String object.
+  // Set up the non-enumerable functions on the String object.
   InstallFunctions($String, DONT_ENUM, $Array(
     "fromCharCode", StringFromCharCode
   ));
 
 
-  // Setup the non-enumerable functions on the String prototype object.
+  // Set up the non-enumerable functions on the String prototype object.
   InstallFunctionsOnHiddenPrototype($String.prototype, DONT_ENUM, $Array(
     "valueOf", StringValueOf,
     "toString", StringToString,
@@ -994,5 +991,4 @@ function SetupString() {
   ));
 }
 
-
-SetupString();
+SetUpString();