Implement exponential back-off mechanism and enforce it at the URLRequestHttpJob level.

net/url_request/url_request_throttler_header_interface.h

+// Copyright (c) 2010 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 NET_URL_REQUEST_URL_REQUEST_THROTTLER_HEADER_INTERFACE_H_
+#define NET_URL_REQUEST_URL_REQUEST_THROTTLER_HEADER_INTERFACE_H_
+
+#include <string>
+
+namespace net {
+
+// Interface to an HTTP header to enforce we have the methods we need.
+class URLRequestThrottlerHeaderInterface {
+ public:
+  virtual ~URLRequestThrottlerHeaderInterface() {}
+
+  // Method that enables us to fetch the header value by its key.
+  // ex: location: www.example.com -> key = "location" value = "www.example.com"
+  // If the key does not exist, it returns an empty string.
+  virtual std::string GetNormalizedValue(const std::string& key) const = 0;
+
+  // Returns the HTTP response code associated with the request.
+  virtual int GetResponseCode() const = 0;
+};
+
+}  // namespace net
+
+#endif  // NET_URL_REQUEST_URL_REQUEST_THROTTLER_HEADER_INTERFACE_H_