Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/mirrors_used_test.dart

Index: tests/compiler/dart2js/mirrors_used_test.dart
diff --git a/tests/compiler/dart2js/mirrors_used_test.dart b/tests/compiler/dart2js/mirrors_used_test.dart
index f1758a3dc685ac0190ac2d9039fa76ae55eea881..515de9decb2800ef549610ae474399e75c5d7206 100644
--- a/tests/compiler/dart2js/mirrors_used_test.dart
+++ b/tests/compiler/dart2js/mirrors_used_test.dart
@@ -97,7 +97,10 @@ void main() {
       compiler.resolution.commonElements.nullClass,
       compiler.resolution.commonElements.listClass
     ];
-    Iterable<String> nativeNames = nativeClasses.map(backend.namer.className);
+    Iterable<String> nativeNames =
+        // `backend.namer.className` returns a Name, but a String is required.
+        // ignore: ARGUMENT_TYPE_NOT_ASSIGNABLE
+        nativeClasses.map((c) => backend.namer.className(c));
     expectedNames = expectedNames.map(backend.namer.asName).toList();
     expectedNames.addAll(nativeNames);
 
@@ -110,7 +113,7 @@ void main() {
       ..addAll(fullEmitter.mangledGlobalFieldNames.keys);
     Expect.setEquals(new Set.from(expectedNames), recordedNames);
 
-    for (var library in compiler.libraryLoader.libraries) {
+    for (dynamic library in compiler.libraryLoader.libraries) {
       library.forEachLocalMember((member) {
         if (member.isClass) {
           if (library == compiler.mainApp && member.name == 'Foo') {