Implement chrome://histograms with network service.

content/browser/histogram_internals_url_loader.h

+// Copyright 2017 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.
+
+#ifndef CONTENT_BROWSER_HISTOGRAM_INTERNALS_URL_LOADER_H_
+#define CONTENT_BROWSER_HISTOGRAM_INTERNALS_URL_LOADER_H_
+
+#include "content/common/url_loader.mojom.h"
+
+namespace content {
+
+// Creates the data for chrome://histograms.
+void StartHistogramInternalsURLLoader(const ResourceRequest& request,
+                                      mojom::URLLoaderClientPtr client);
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_HISTOGRAM_INTERNALS_URL_LOADER_H_