Remove Compiler.mainApp and Compiler.mainFunction

tests/compiler/dart2js/value_range3_test.dart

Index: tests/compiler/dart2js/value_range3_test.dart
diff --git a/tests/compiler/dart2js/value_range3_test.dart b/tests/compiler/dart2js/value_range3_test.dart
index 851a36a222ae359607938553382607db2f201b5c..e0f6c5f5981552fecfe912402f123cf224b94782 100644
--- a/tests/compiler/dart2js/value_range3_test.dart
+++ b/tests/compiler/dart2js/value_range3_test.dart
@@ -26,7 +26,7 @@ main() {
   asyncTest(() async {
     var result = await runCompiler(memorySourceFiles: MEMORY_SOURCE_FILES);
     var compiler = result.compiler;
-    var element = compiler.mainFunction;
+    var element = compiler.frontendStrategy.elementEnvironment.mainFunction;
     var code = compiler.backend.getGeneratedCode(element);
     Expect.isFalse(code.contains('ioore'));
   });