Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/source_map_name_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.
 
 library source_map_name_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
@@ skipping 64 matching lines @@
   String name = computeElementNameForSourceMaps(element);
   Expect.equals(expectedName, name,
       "Unexpected name '$name' for $element, expected '$expectedName'.");
 }
 
 main() {
   asyncTest(() async {
     CompilationResult result =
         await runCompiler(memorySourceFiles: {'main.dart': SOURCE});
     Compiler compiler = result.compiler;
-    LibraryElement mainApp = compiler.mainApp;
+    LibraryElement mainApp =
+        compiler.frontendStrategy.elementEnvironment.mainLibrary;
 
     Element lookup(String name) {
       Element element;
       int dotPosition = name.indexOf('.');
       if (dotPosition != -1) {
         String clsName = name.substring(0, dotPosition);
         ClassElement cls = mainApp.find(clsName);
         Expect.isNotNull(cls, "Class '$clsName' not found.");
         element = cls.localLookup(name.substring(dotPosition + 1));
       } else {
@@ skipping 51 matching lines @@
     checkName('Class.instanceAnonymous',
         ['Class.instanceAnonymous.<anonymous function>']);
     checkName('Class.instanceLocal', ['Class.instanceLocal.localMethod']);
     checkName('Class.instanceNestedLocal', [
       'Class.instanceNestedLocal.localMethod',
       'Class.instanceNestedLocal.localMethod.<anonymous function>',
       'Class.instanceNestedLocal.localMethod.nestedLocalMethod'
     ]);
   });
 }