Allow fallback from https to http for component update checks.

components/update_client/update_engine.h

 // 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.
 
 #ifndef COMPONENTS_UPDATE_CLIENT_UPDATE_ENGINE_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_ENGINE_H_
 
 #include <list>
 #include <queue>
 #include <set>
@@ skipping 45 matching lines @@
   bool GetUpdateState(const std::string& id, CrxUpdateItem* update_state);
 
   void Update(bool is_foreground,
               const std::vector<std::string>& ids,
               const UpdateClient::CrxDataCallback& crx_data_callback,
               const CompletionCallback& update_callback);
 
  private:
   void UpdateComplete(UpdateContext* update_context, int error);
 
+  // Returns true if the update engine rejects this update call because it
+  // occurs too soon.
+  bool IsThrottled(bool is_foreground) const;
+
   base::ThreadChecker thread_checker_;
 
   scoped_refptr<Configurator> config_;
 
   UpdateChecker::Factory update_checker_factory_;
   CrxDownloader::Factory crx_downloader_factory_;
 
   // TODO(sorin): refactor as a ref counted class.
   PingManager* ping_manager_;  // Not owned by this class.
 
   // Called when CRX state changes occur.
   const NotifyObserversCallback notify_observers_callback_;
 
   // Contains the contexts associated with each update in progress.
   std::set<UpdateContext*> update_contexts_;
 
+  // Implements a rate limiting mechanism for background update checks. Has the
+  // effect of rejecting the update call if the update call occurs before
+  // a certain time, which is negotiated with the server as part of the
+  // update protocol. See the comments for X-Retry-After header.
+  base::Time throttle_updates_until_;
+
   DISALLOW_COPY_AND_ASSIGN(UpdateEngine);
 };
 
 // TODO(sorin): consider making this a ref counted type.
 struct UpdateContext {
   UpdateContext(
       const scoped_refptr<Configurator>& config,
       bool is_foreground,
       const std::vector<std::string>& ids,
       const UpdateClient::CrxDataCallback& crx_data_callback,
@@ skipping 36 matching lines @@
 
   PingManager* ping_manager;  // Not owned by this class.
 
   scoped_ptr<Action> current_action;
 
   // TODO(sorin): use a map instead of vector.
   std::vector<CrxUpdateItem*> update_items;
 
   // Contains the ids of the items to update.
   std::queue<std::string> queue;
+
+  // The time in seconds to wait until doing further update checks.
+  int retry_after_sec_;
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_ENGINE_H_