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

tests/html/native_gc_test.dart

-#library('NativeGCTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library NativeGCTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   test('EventListener', () {
       final int N = 1000000;
       final int M = 1000;
 
       var div;
       for (int i = 0; i < M; ++i) {
@@ skipping 29 matching lines @@
     testDiv.on.click.add(expectAsync1((e) {}));
     window.postMessage('test', '*');
   });
 }
 
 void triggerMajorGC() {
   List list = new List(1000000);
   Element div = new DivElement();
   div.on.click.add((e) => print(list[0]));
 }