Move minitest.dart into the expect package.

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

 import 'dart:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 main() {
   CanvasElement canvas;
 
   canvas = new Element.tag('canvas');
   canvas.attributes['width'] = '100';
   canvas.attributes['height'] = '100';
   document.body.append(canvas);
 
   var isCanvasRenderingContext = predicate((x) => x is CanvasRenderingContext,
@@ skipping 54 matching lines @@
     expect(bytes, isNotCanvasElement);
     expect(bytes, isNotImageData);
     expect(bytes, isIntList);
 
     // FIXME: Ensure this is an SpanElement when we next update
     // WebKit IDL.
     var span = new Element.tag('span');
     expect(span, isElement);
   });
 }