Move minitest.dart into the expect package.

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

 import 'dart:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 main() {
   var isRectList =
       predicate((x) => x is List<Rectangle>, 'is a List<Rectangle>');
 
   insertTestDiv() {
     var element = new Element.tag('div');
     element.innerHtml = r'''
     A large block of text should go here. Click this
     block of text multiple times to see each line
     highlight with every click of the mouse button.
     ''';
     document.body.append(element);
     return element;
   }
 
   test("ClientRectList test", () {
     insertTestDiv();
     var range = new Range();
     var rects = range.getClientRects();
     expect(rects, isRectList);
   });
 }