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

tests/html/htmlcollection_test.dart

-#library('ElementListTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library ElementListTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 // Test that List<Element> implements List<T>
 main() {
   Element insertTestDiv() {
     Element element = new Element.tag('div');
     element.innerHTML = r"""
 <div id='allChecked'>
 <input type="checkbox" name="c1" value="1" checked="yes">
 <input type="checkbox" name="c2" value="2" checked="yes">
 <input type="checkbox" name="c3" value="3" checked="yes">
@@ skipping 253 matching lines @@
     expect(someChecked.lastIndexOf(someChecked[3], 2), -1);
 
     expect(someChecked.lastIndexOf(noneChecked[0], 3), -1);
     expect(noneChecked.lastIndexOf(someChecked[0], 3), -1);
     expect(someChecked.lastIndexOf(noneChecked[1], 3), -1);
     expect(noneChecked.lastIndexOf(someChecked[1], 3), -1);
 
     root.remove();
   });
 }