Refactor script position calculation

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 1932 matching lines @@
   var location = this.sourceLocation();
   if (location) {
     return location.column;
   }
 };
 
 
 FrameMirror.prototype.sourceLineText = function() {
   var location = this.sourceLocation();
   if (location) {
-    return location.sourceText();
+    return location.sourceText;
   }
 };
 
 
 FrameMirror.prototype.scopeCount = function() {
   return this.details_.scopeCount();
 };
 
 
 FrameMirror.prototype.scope = function(index) {
@@ skipping 1076 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;
 });
 })