Add test of unittests.

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.
 
 // 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 CompilerImpl;
 import 'memory_compiler.dart';
 import 'package:compiler/src/cps_ir/cps_ir_nodes.dart' as ir;
 import 'package:compiler/src/cps_ir/cps_ir_nodes_sexpr.dart' as ir;
 import 'package:compiler/src/js/js.dart' as js;
+import 'package:compiler/src/js_backend/js_backend.dart';
 import 'package:compiler/src/elements/elements.dart';
 
 const String TEST_MAIN_FILE = 'test.dart';
 
 class TestEntry {
   final String source;
   final List<String> expectation;
   final String elementName;
 
   const TestEntry(this.source, this.expectation)
@@ skipping 44 matching lines @@
       ir.FunctionDefinition irNodeForMain;
 
       void cacheIrNodeForMain(Element function, ir.FunctionDefinition irNode) {
         if (function == compiler.mainFunction) {
           assert(irNodeForMain == null);
           irNodeForMain = irNode;
         }
       }
 
       Uri uri = Uri.parse('memory:$TEST_MAIN_FILE');
-      compiler.backend.functionCompiler.cpsBuilderTask.builderCallback =
-          cacheIrNodeForMain;
+      JavaScriptBackend backend = compiler.backend;
+      var functionCompiler = backend.functionCompiler;
+      functionCompiler.cpsBuilderTask.builderCallback = cacheIrNodeForMain;
 
       return compiler.run(uri).then((bool success) {
         Expect.isTrue(success);
 
         IrSourceInformationVisitor irVisitor = new IrSourceInformationVisitor();
         irNodeForMain.accept(irVisitor);
 
         js.Node jsNode = getJsNodeForElement(compiler, compiler.mainFunction);
         JsSourceInformationVisitor jsVisitor = new JsSourceInformationVisitor();
         jsNode.accept(jsVisitor);
@@ skipping 48 matching lines @@
   print('Hello');
   print('World');
 }
 """, const ['memory:test.dart:[2,3]',
             'memory:test.dart:[3,3]']),
 ];
 
 void main() {
   runTests(tests);
 }