Adds UMA to measure when the data reduction proxy via header is missing

components/data_reduction_proxy/common/data_reduction_proxy_headers_test_utils.cc

+// Copyright 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.
+
+#include "components/data_reduction_proxy/common/data_reduction_proxy_headers_test_utils.h"
+
+#include <algorithm>
+
+namespace data_reduction_proxy {
+
+void HeadersToRaw(std::string* headers) {
+  std::replace(headers->begin(), headers->end(), '\n', '\0');
+  if (!headers->empty())
+    *headers += '\0';
+}
+
+}  // namespace data_reduction_proxy