Allow fallback from https to http for component update checks.

components/update_client/update_client.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_CLIENT_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_H_
 
 #include <stdint.h>
 #include <string>
 #include <vector>
@@ skipping 125 matching lines @@
 
 namespace update_client {
 
 class Configurator;
 struct CrxUpdateItem;
 
 enum Error {
   ERROR_UPDATE_INVALID_ARGUMENT = -1,
   ERROR_UPDATE_IN_PROGRESS = 1,
   ERROR_UPDATE_CANCELED = 2,
+  ERROR_UPDATE_RETRY_LATER = 3,
 };
 
 // Defines an interface for a generic CRX installer.
 class CrxInstaller : public base::RefCountedThreadSafe<CrxInstaller> {
  public:
   // Called on the main thread when there was a problem unpacking or
   // verifying the CRX. |error| is a non-zero value which is only meaningful
   // to the caller.
   virtual void OnUpdateError(int error) = 0;
 
@@ skipping 164 matching lines @@
   virtual ~UpdateClient() {}
 };
 
 // Creates an instance of the update client.
 scoped_refptr<UpdateClient> UpdateClientFactory(
     const scoped_refptr<Configurator>& config);
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_H_