Import polymer in a single place and remove d3 hacks

tracing/tracing/ui/base/d3_preload.js

Index: tracing/tracing/ui/base/d3_preload.js
diff --git a/tracing/tracing/ui/base/d3_preload.js b/tracing/tracing/ui/base/d3_preload.js
new file mode 100644
index 0000000000000000000000000000000000000000..57548f1d175dfe344687cf2ac7ce48c349b7e223
--- /dev/null
+++ b/tracing/tracing/ui/base/d3_preload.js
@@ -0,0 +1,11 @@
+/* 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. */
+'use strict';
+
+(function(window) {
+  window.define = function(x) {

[aiolos (Not reviewing), 2016/08/22 23:19:27]

Do we need to worry about window.define already being defined in js somewhere
else, and us breaking them when we set it to undefined after we load d3? I
didn't see window.define being used elsewhere in tracing, so I'm hoping not.

[eakuefner, 2016/08/23 22:41:39]

I don't think so, because window.define is used by require.js. Although tracing
is available as a node module, people who are using it in that context are
unlikely to import d3, so I think this should be fine.

+    window.d3 = x;
+  };
+  window.define.amd = true;
+})(this);