Add a NavigationThrottle to the public content/ interface

content/public/browser/navigation_throttle.cc

+// Copyright 2015 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 "content/public/browser/navigation_throttle.h"
+
+namespace content {
+
+NavigationThrottle::NavigationThrottle(NavigationHandle* navigation_handle)
+    : navigation_handle_(navigation_handle) {}
+
+NavigationThrottle::~NavigationThrottle() {}
+
+NavigationThrottle::ThrottleCheckResult NavigationThrottle::WillStartRequest() {
+  return NavigationThrottle::PROCEED;
+}
+
+NavigationThrottle::ThrottleCheckResult
+NavigationThrottle::WillRedirectRequest() {
+  return NavigationThrottle::PROCEED;
+}
+
+}  // namespace content