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

tests/html/client_rect_test.dart

-#library('ClientRectTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library ClientRectTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
 
   var isClientRectList =
       predicate((x) => x is List<ClientRect>, 'is a List<ClientRect>');
 
   insertTestDiv() {
     var element = new Element.tag('div');
     element.innerHTML = r'''
     A large block of text should go here. Click this
     block of text multiple times to see each line
     highlight with every click of the mouse button.
     ''';
     document.body.nodes.add(element);
     return element;
   }
 
   useHtmlConfiguration();
 
    test("ClientRectList test", () {
     insertTestDiv();
     var range = document.createRange();
     var rects = range.getClientRects();
     expect(rects, isClientRectList);
   });
 }