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

tests/html/css_test.dart

-#library('CSSTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library CSSTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
   test('CSSMatrix', () {
     CSSMatrix matrix1 = new CSSMatrix();
     expect(matrix1.m11.round(), equals(1));
     expect(matrix1.m12.round(), isZero);
 
     CSSMatrix matrix2 = new CSSMatrix('matrix(1, 0, 0, 1, -835, 0)');
     expect(matrix2.a.round(), equals(1));
@@ skipping 19 matching lines @@
     point.y = 100;
     checkPoint(5, 100, point);
     checkPoint(254, 196, window.webkitConvertPointFromNodeToPage(element, point));
   });
 }
 
 void checkPoint(expectedX, expectedY, Point point) {
   expect(point.x.round(), equals(expectedX), reason: 'Wrong point.x');
   expect(point.y.round(), equals(expectedY), reason: 'Wrong point.y');
 }