Add a histogram (Net.PacResultForStrippedUrl) that estimates how often PAC scripts depend on the UR…

net/data/proxy_resolver_v8_tracing_unittest/return_url_as_proxy.js

+// 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.
+
+// This proxy script returns a proxy list that encodes the URL that was passed
+// in.
+
+function convertUrlToHostname(url) {
+  // Turn the URL into something that resembles a hostname.
+  var result = encodeURIComponent(url);
+  return result.replace(/%/g, "x");
+}
+
+function FindProxyForURL(url, host) {
+  return "PROXY " + convertUrlToHostname(url) + ":99";
+}