Restructure pkg/unittest and pkg/webdriver to follow the pub conventions.

tests/html/utils.dart

-#library('TestUtils');
-#import('../../pkg/unittest/unittest.dart');
+library TestUtils;
+import '../../pkg/unittest/lib/unittest.dart';
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
  * Detects cycles and DAG structure in Maps and Lists.
  */
 verifyGraph(expected, actual) {
   var eItems = [];
   var aItems = [];
 
   message(path, reason) => path == ''
@@ skipping 48 matching lines @@
         }
       }
       return;
     }
 
     expect(false, isTrue, reason: 'Unhandled type: $expected');
   }
 
   walk('', expected, actual);
 }