Implement support for fallback update check urls in the component updater

components/component_updater/request_sender.h

Index: components/component_updater/request_sender.h
diff --git a/components/component_updater/request_sender.h b/components/component_updater/request_sender.h
new file mode 100644
index 0000000000000000000000000000000000000000..77d9964eb0f6215029a16aa67a0d03b5c1b419b9
--- /dev/null
+++ b/components/component_updater/request_sender.h
@@ -0,0 +1,61 @@
+// 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.
+
+#ifndef COMPONENTS_COMPONENT_UPDATER_REQUEST_SENDER_H_
+#define COMPONENTS_COMPONENT_UPDATER_REQUEST_SENDER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "net/url_request/url_fetcher_delegate.h"
+#include "url/gurl.h"
+
+namespace net {
+class URLFetcher;
+}
+
+namespace component_updater {
+
+class Configurator;
+
+// Sends a request to one of the urls provided. The class implements a chain
+// of responsibility design pattern, where the urls are tried in the order they
+// are specified, until the request to one of them succeeds or all have failed.
+class RequestSender : public net::URLFetcherDelegate {
+ public:
+  // The |source| refers to the fetcher object used to make the request. This
+  // parameter can be NULL in some error cases.
+  typedef base::Callback<void(const net::URLFetcher* source)>
+      RequestSenderCallback;
+
+  explicit RequestSender(const Configurator& config);
+  virtual ~RequestSender();
+
+  void Send(const std::string& request_string,
+            const std::vector<GURL>& urls,
+            const RequestSenderCallback& request_sender_callback);
+
+ private:
+  void SendInternal();
+
+  // Overrides for URLFetcherDelegate.
+  virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
+
+  const Configurator& config_;
+  std::vector<GURL> urls_;
+  std::vector<GURL>::const_iterator cur_url_;
+  scoped_ptr<net::URLFetcher> url_fetcher_;
+  std::string request_string_;
+  RequestSenderCallback request_sender_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(RequestSender);
+};
+
+}  // namespace component_updater
+
+#endif  // COMPONENTS_COMPONENT_UPDATER_REQUEST_SENDER_H_