Add a command line option to use the new CPS based backend.

tests/compiler/dart2js/js_backend_cps_ir_source_information_test.dart

 // Copyright (c) 2015, 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.
-// VMOptions=-DUSE_CPS_IR=true
 
 // Test that the CPS IR code generator generates source information.
 
 library source_information_tests;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/apiimpl.dart'
        show Compiler;
 import 'memory_compiler.dart';
@@ skipping 46 matching lines @@
 
   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();
 }
 
 runTests(List<TestEntry> tests) {
-  Expect.isTrue(const bool.fromEnvironment("USE_CPS_IR"),
-      'Run with USE_CPS_IR=true');
-
   for (TestEntry test in tests) {
     Map files = {TEST_MAIN_FILE: test.source};
     asyncTest(() {
-      Compiler compiler = compilerFor(files);
+      Compiler compiler = compilerFor(files, options: <String>['--use-cps-ir']);
       Uri uri = Uri.parse('memory:$TEST_MAIN_FILE');
       return compiler.run(uri).then((bool success) {
         Expect.isTrue(success);
 
         ir.Node irNode = getIrNodeForElement(compiler, compiler.mainFunction);
         IrSourceInformationVisitor irVisitor = new IrSourceInformationVisitor();
         irNode.accept(irVisitor);
 
         js.Node jsNode = getJsNodeForElement(compiler, compiler.mainFunction);
         JsSourceInformationVisitor jsVisitor = new JsSourceInformationVisitor();
@@ skipping 38 matching lines @@
   processInvokeStatic(ir.InvokeStatic node) {
     sourceInformation.add('${node.sourceInformation}');
   }
 }
 
 const List<TestEntry> tests = const [
   const TestEntry("""
 main() { print('Hello World'); }
 """, const ['memory:test.dart:[1,10]']),
 const TestEntry("""
-main() { 
+main() {
   print('Hello');
   print('World');
 }
 """, const ['memory:test.dart:[2,3]',
             'memory:test.dart:[3,3]']),
 ];
 
 void main() {
   runTests(tests);
 }