Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/mirrors_used_test.dart

 // Copyright (c) 2013, 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 @MirrorsUsed annotation suppress hints and that only
 /// requested elements are retained for reflection.
 library dart2js.test.mirrors_used_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 95 matching lines @@
     full.Emitter fullEmitter = backend.emitter.emitter;
     Set recordedNames = new Set()
       ..addAll(fullEmitter.recordedMangledNames)
       ..addAll(fullEmitter.mangledFieldNames.keys)
       ..addAll(fullEmitter.mangledGlobalFieldNames.keys);
     Expect.setEquals(new Set.from(expectedNames), recordedNames);
 
     for (var library in compiler.libraryLoader.libraries) {
       library.forEachLocalMember((member) {
         if (member.isClass) {
-          if (library == compiler.mainApp && member.name == 'Foo') {
+          if (library ==
+                  compiler.frontendStrategy.elementEnvironment.mainLibrary &&
+              member.name == 'Foo') {
             Expect.isTrue(
                 compiler.backend.mirrorsData
                     .isClassAccessibleByReflection(member),
                 '$member');
             member.forEachLocalMember((classMember) {
               Expect.isTrue(
                   compiler.backend.mirrorsData
                       .isMemberAccessibleByReflection(classMember),
                   '$classMember');
             });
@@ skipping 78 matching lines @@
 library lib;
 
 import 'dart:mirrors';
 
 useReflect(type) {
   print(new Symbol('Foo'));
   print(MirrorSystem.getName(reflectClass(type).owner.qualifiedName));
 }
 """,
 };