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

tests/html/svg_2_test.dart

-#library('SVG2Test');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library SVG2Test;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 // Test that SVG elements explicitly implement the IDL interfaces (is-checks
 // only, see SVGTest3 for behavioural tests).
 
 main() {
 
   insertTestDiv() {
     var element = new Element.tag('div');
     element.innerHTML = r'''
 <svg id='svg1' width='200' height='100'>
@@ skipping 41 matching lines @@
       expect(r, isSVGLocatable);
 
       // Interfaces not implemented.
       expect(r, isNot(isSVGNumber));
       expect(r, isNot(isSVGRect));
       expect(r, isNot(isSVGSVGElement));
 
       div.remove();
     });
 }