Move unittest from lib to pkg.

tests/html/canvas_using_html_test.dart

 #library('CanvasUsingHtmlTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html', prefix: 'html');
 #import('dart:html');
 
 // Version of Canvas test that implicitly uses dart:html library via unittests.
 
 main() {
   CanvasElement canvas;
   CanvasRenderingContext2D context;
 
   canvas = new Element.tag('canvas');
@@ skipping 34 matching lines @@
     ImageData image = context.createImageData(canvas.width,
                                               canvas.height);
     Uint8ClampedArray bytes = image.data;
 
     // FIXME: uncomment when numeric index getters are supported.
     //var byte = bytes[0];
 
     expect(bytes, hasLength(40000));
   });
 }