Move minitest.dart into the expect package.

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

 import 'dart:html';
 
-import 'package:minitest/minitest.dart';
+import 'package:expect/minitest.dart';
 
 main() {
   var isElement = predicate((x) => x is Element, 'is an Element');
   var isDivElement = predicate((x) => x is DivElement, 'is a DivElement');
   var isAnchorElement =
       predicate((x) => x is AnchorElement, 'is an AnchorElement');
   var isUnknownElement =
       predicate((x) => x is UnknownElement, 'is UnknownElement');
 
   var inscrutable;
@@ skipping 60 matching lines @@
 
     test('typeTest2', () {
       inscrutable = inscrutable(inscrutable);
       // XML document.
       var doc3 = document.implementation.createDocument(null, 'report', null);
       expect(doc3 is HtmlDocument, false);
       expect(inscrutable(doc3) is HtmlDocument, false);
     });
   });
 }