Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/deferred_not_in_main_test.dart

 // Copyright (c) 2014, 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 of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:expect/expect.dart';
 import 'memory_compiler.dart';
 
 void main() {
   deferredTest1();
   deferredTest2();
 }
 
 void deferredTest1() {
   asyncTest(() async {
     CompilationResult result = await runCompiler(memorySourceFiles: TEST1);
     Compiler compiler = result.compiler;
 
     lookupLibrary(name) {
       return compiler.libraryLoader.lookupLibrary(Uri.parse(name));
     }
 
-    var main = compiler.mainFunction;
+    var main = compiler.frontendStrategy.elementEnvironment.mainFunction;
     var outputUnitForElement = compiler.deferredLoadTask.outputUnitForElement;
 
     var mainOutputUnit = compiler.deferredLoadTask.mainOutputUnit;
     var backend = compiler.backend;
     var lib1 = lookupLibrary("memory:lib1.dart");
     var lib2 = lookupLibrary("memory:lib2.dart");
     var foo1 = lib1.find("foo1");
     var foo2 = lib2.find("foo2");
 
     Expect.notEquals(mainOutputUnit, outputUnitForElement(foo2));
   });
 }
 
 void deferredTest2() {
   asyncTest(() async {
     CompilationResult result = await runCompiler(memorySourceFiles: TEST2);
     Compiler compiler = result.compiler;
 
     lookupLibrary(name) {
       return compiler.libraryLoader.lookupLibrary(Uri.parse(name));
     }
 
-    var main = compiler.mainFunction;
+    var main = compiler.frontendStrategy.elementEnvironment.mainFunction;
     var outputUnitForElement = compiler.deferredLoadTask.outputUnitForElement;
 
     var mainOutputUnit = compiler.deferredLoadTask.mainOutputUnit;
     var shared = lookupLibrary("memory:shared.dart");
     var a = shared.find("A");
 
     Expect.equals(mainOutputUnit, outputUnitForElement(a));
   });
 }
 
@@ skipping 47 matching lines @@
 import 'shared.dart';
 
 toto() { print(new A()); }
 """,
   "shared.dart": """
 class A {}
 class B extends A {}
 foo(B b) => null;
 """,
 };