Format all tests.

tests/language_strong/list_mixin_test.dart

 import 'dart:collection';
 import 'package:expect/expect.dart';
 
 class MyList extends ListBase {
   int get length => 4;
   set length(int x) {}
-  int operator[](int x) => 42;
-  void operator[]=(int x, val) {}
+  int operator [](int x) => 42;
+  void operator []=(int x, val) {}
 }
 
 main() {
   var x = new MyList();
   int z = 0;
-  x.forEach((y) { z += y; });
+  x.forEach((y) {
+    z += y;
+  });
   Expect.equals(z, 4 * 42);
 }