[runtime] Fully remove RUNTIME_ASSERT for good.

src/debug/mirrors.js

 // Copyright 2006-2012 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.
 
 (function(global, utils) {
 "use strict";
 
 // ----------------------------------------------------------------------------
 // Imports
 
@@ skipping 2324 matching lines @@
   return this.script_.id;
 };
 
 
 ScriptMirror.prototype.source = function() {
   return this.script_.source;
 };
 
 
 ScriptMirror.prototype.setSource = function(source) {
+  if (!IS_STRING(source)) throw MakeError(kDebugger, "Source is not a string");
   %DebugSetScriptSource(this.script_, source);
 };
 
 
 ScriptMirror.prototype.lineOffset = function() {
   return this.script_.line_offset;
 };
 
 
 ScriptMirror.prototype.columnOffset = function() {
@@ skipping 696 matching lines @@
 // Functions needed by the debugger runtime.
 utils.InstallFunctions(utils, DONT_ENUM, [
   "ClearMirrorCache", ClearMirrorCache
 ]);
 
 // Export to debug.js
 utils.Export(function(to) {
   to.MirrorType = MirrorType;
 });
 })