Import polymer in a single place and remove d3 hacks

tracing/tracing/ui/base/polymer_postload.html

Index: tracing/tracing/ui/base/polymer_postload.html
diff --git a/tracing/tracing/ui/base/webcomponents.html b/tracing/tracing/ui/base/polymer_postload.html
similarity index 55%
rename from tracing/tracing/ui/base/webcomponents.html
rename to tracing/tracing/ui/base/polymer_postload.html
index c2805157424b52d096f8e3a864272bf4e7c0f432..fc93631bb88c4783c69b90d138aa56ca38d084c7 100644
--- a/tracing/tracing/ui/base/webcomponents.html
+++ b/tracing/tracing/ui/base/polymer_postload.html
@@ -4,4 +4,10 @@ Copyright 2016 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.
 -->
-<script src="/components/webcomponentsjs/webcomponents-lite.js">
+<script>
+'use strict';
+
+if (!Polymer.Settings.useNativeShadow) {
+  tr.b.showPanic('Polymer error', 'base only works in shadow mode');
+}
+</script>