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

tests/html/audiobuffersourcenode_test.dart

-#library('AudioBufferSourceNodeTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library AudioBufferSourceNodeTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
 
   useHtmlConfiguration();
 
   test('createBuffer', () {
       var ctx = new AudioContext();
       AudioBufferSourceNode node = ctx.createBufferSource();
       node.start(ctx.currentTime, 0, 2);
       node.stop(ctx.currentTime + 2);
       expect(node is AudioBufferSourceNode, isTrue);
   });
 }