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

net/data/proxy_resolver_v8_tracing_unittest/error_depending_on_url.js

Index: net/data/proxy_resolver_v8_tracing_unittest/error_depending_on_url.js
diff --git a/net/data/proxy_resolver_v8_tracing_unittest/error_depending_on_url.js b/net/data/proxy_resolver_v8_tracing_unittest/error_depending_on_url.js
new file mode 100644
index 0000000000000000000000000000000000000000..42256ebc66e777333848e661e4b185952fda1027
--- /dev/null
+++ b/net/data/proxy_resolver_v8_tracing_unittest/error_depending_on_url.js
@@ -0,0 +1,13 @@
+// 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 throws an error if the URL does not contain the substring
+// "DontThrowError".
+function FindProxyForURL(url, host) {
+  if (url.indexOf("DontThrowError") == -1) {
+    ErrorUndefinedFunction();
+    return -1;
+  }
+  return "PROXY foopy:42";
+}