Move minitest.dart into the expect package.

pkg/dev_compiler/test/codegen/lib/html/cross_frame_test.dart

 import 'dart:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 main() {
   var isWindowBase = predicate((x) => x is WindowBase, 'is a WindowBase');
   var isWindow = predicate((x) => x is Window, 'is a Window');
   var isLocationBase = predicate((x) => x is LocationBase, 'is a LocationBase');
   var isLocation =
       predicate((x) => x is Location, 'is a Location');
   var isHistoryBase = predicate((x) => x is HistoryBase, 'is a HistoryBase');
   var isHistory = predicate((x) => x is History, 'is a History');
 
@@ skipping 49 matching lines @@
 
       // Valid methods.
       frameHistory.forward();
 
       expect(() => frameHistory.length, throws);
 
       final frameParentHistory = iframe.contentWindow.parent.history;
       expect(frameParentHistory, isHistory);
     });
 }