Import polymer in a single place and remove d3 hacks

tracing/tracing/ui/base/d3_postload.js

Index: tracing/tracing/ui/base/d3_postload.js
diff --git a/tracing/tracing/ui/tracks/rect_track.css b/tracing/tracing/ui/base/d3_postload.js
similarity index 54%
copy from tracing/tracing/ui/tracks/rect_track.css
copy to tracing/tracing/ui/base/d3_postload.js
index 0467c91562cc178d64c3c6a735bf7e9db6d093ac..94cefdb15f943465c75164f719d56fc1d0677492 100644
--- a/tracing/tracing/ui/tracks/rect_track.css
+++ b/tracing/tracing/ui/base/d3_postload.js
@@ -1,8 +1,8 @@
 /* Copyright (c) 2014 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
+ * found in the LICENSE file. */
+'use strict';
 
-.rect-track {
-  height: 18px;
-}
+(function(window) {
+  window.define = undefined;
+}).call(this, this);