Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/type_representation_test.dart

Index: tests/compiler/dart2js/type_representation_test.dart
diff --git a/tests/compiler/dart2js/type_representation_test.dart b/tests/compiler/dart2js/type_representation_test.dart
index 0a345a6b06873f3c61592df08b07f048031151a9..a2782c72fe2def902f7b71abac19fb53e72abdbe 100644
--- a/tests/compiler/dart2js/type_representation_test.dart
+++ b/tests/compiler/dart2js/type_representation_test.dart
@@ -44,7 +44,10 @@ void testTypeRepresentations() {
       m9(int a, String b, {List<int> c, d}) {}
       m10(void f(int a, [b])) {}
       """).then((env) {
-        var closedWorldRefiner = env.compiler.closeResolution();
+        var elementEnvironment =
+            env.compiler.frontendStrategy.elementEnvironment;
+        var closedWorldRefiner =
+            env.compiler.closeResolution(elementEnvironment.mainFunction);
         var closedWorld = closedWorldRefiner.closedWorld;
         env.compiler.enqueuer.createCodegenEnqueuer(closedWorld);
         env.compiler.backend.onCodegenStart(