Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/expect_annotations_test.dart

Index: tests/compiler/dart2js/expect_annotations_test.dart
diff --git a/tests/compiler/dart2js/expect_annotations_test.dart b/tests/compiler/dart2js/expect_annotations_test.dart
index 83e1de3523183743129a96774df99821992bceba..c2b39f0a75831bf134b90523b9813de554682e18 100644
--- a/tests/compiler/dart2js/expect_annotations_test.dart
+++ b/tests/compiler/dart2js/expect_annotations_test.dart
@@ -83,7 +83,8 @@ main() {
         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),