Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/expect_annotations_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.
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/js_backend/js_backend.dart';
 import 'package:compiler/src/types/types.dart';
@@ skipping 65 matching lines @@
             expectedReturnType, simplify(type, closedWorld), "$function");
       }
     }
 
     void test(String name,
         {bool expectNoInline: false,
         bool expectTrustTypeAnnotations: false,
         TypeMask expectedParameterType: null,
         TypeMask expectedReturnType: null,
         bool expectAssumeDynamic: false}) {
-      LibraryElement mainApp = compiler.mainApp;
+      LibraryElement mainApp =
+          compiler.frontendStrategy.elementEnvironment.mainLibrary;
       MethodElement method = mainApp.find(name);
       Expect.isNotNull(method);
       Expect.equals(expectNoInline, backend.optimizerHints.noInline(method),
           "Unexpected annotation of @NoInline on '$method'.");
       Expect.equals(
           expectTrustTypeAnnotations,
           backend.optimizerHints.trustTypeAnnotations(method),
           "Unexpected annotation of @TrustTypeAnnotations on '$method'.");
       Expect.equals(
           expectAssumeDynamic,
@@ skipping 23 matching lines @@
         expectNoInline: true,
         expectTrustTypeAnnotations: true,
         expectedParameterType: jsStringType,
         expectedReturnType: jsIntType);
     test('methodAssumeDynamicTrustTypeAnnotations',
         expectAssumeDynamic: true,
         expectTrustTypeAnnotations: true,
         expectedParameterType: coreStringType);
   });
 }