Convert unittest to use "package:" imports.

pkg/unittest/test/mock_regexp_negative_test.dart

Index: pkg/unittest/test/mock_regexp_negative_test.dart
diff --git a/pkg/unittest/test/mock_regexp_negative_test.dart b/pkg/unittest/test/mock_regexp_negative_test.dart
index 91811f5dc70f838518ab21095a4fceba3d6bef2e..c682e9b190fd4298d2a69521e5c36ffe4b5b5a1f 100644
--- a/pkg/unittest/test/mock_regexp_negative_test.dart
+++ b/pkg/unittest/test/mock_regexp_negative_test.dart
@@ -3,14 +3,14 @@
 // BSD-style license that can be found in the LICENSE file.
 
 library mock_regexp_negative_test;
-import '../../../pkg/unittest/lib/unittest.dart';
-import '../../../pkg/unittest/lib/mock.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/mock.dart';
 
 main() {
   test('Mocking: RegExp CallMatcher bad', () {
-    var m = new Mock();           
-    m.when(callsTo(matches('^[A-Z]'))).          
-           alwaysThrow('Method names must start with lower case.');      
-    m.Test();         
+    var m = new Mock();
+    m.when(callsTo(matches('^[A-Z]'))).
+           alwaysThrow('Method names must start with lower case.');
+    m.Test();
   });
 }