Base JavaScript code position computation on JavaScript tracer.

tests/compiler/dart2js/cps_ir/runner.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test that the CPS IR code generator compiles programs and produces the
 // the expected output.
 
 import 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
@@ skipping 100 matching lines @@
 
 const String TEST_MAIN_FILE = 'test.dart';
 
 String _formatTest(Map test) {
   return test[TEST_MAIN_FILE];
 }
 
 String _getCodeForMain(CompilerImpl compiler) {
   Element mainFunction = compiler.mainFunction;
   js.Node ast = compiler.enqueuer.codegen.generatedCode[mainFunction];
-  return js.prettyPrint(ast, compiler).getText();
+  return js.prettyPrint(ast, compiler);
 }
 
 String _getCodeForMethod(CompilerImpl compiler,
                         String name) {
   Element foundElement;
   for (Element element in compiler.enqueuer.codegen.generatedCode.keys) {
     if (element.toString() == name) {
       if (foundElement != null) {
         Expect.fail('Multiple compiled elements are called $name');
       }
       foundElement = element;
     }
   }
 
   if (foundElement == null) {
     Expect.fail('There is no compiled element called $name');
   }
 
   js.Node ast = compiler.enqueuer.codegen.generatedCode[foundElement];
-  return js.prettyPrint(ast, compiler).getText();
+  return js.prettyPrint(ast, compiler);
 }