[OfflinePages] Improve visiblity/handling of "Loading not started" case

components/offline_pages/core/background/offliner.h

 // Copyright 2016 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_OFFLINE_PAGES_CORE_BACKGROUND_OFFLINER_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_BACKGROUND_OFFLINER_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 22 matching lines @@
     // Loading was canceled.
     LOADING_CANCELED = 4,
     // Loader failed to load page.
     LOADING_FAILED = 5,
     // Failed to save loaded page.
     SAVE_FAILED = 6,
     // Foreground transition canceled request.
     FOREGROUND_CANCELED = 7,
     // RequestCoordinator canceled request attempt per time limit.
     REQUEST_COORDINATOR_TIMED_OUT = 8,
-    // The loader did not accept/start the request.
-    LOADING_NOT_STARTED = 9,
+    // Deprecated. The RequestCoordinator did not start loading the request.
+    DEPRECATED_LOADING_NOT_STARTED = 9,
     // Loader failed with hard error so should not retry the request.
     LOADING_FAILED_NO_RETRY = 10,
     // Loader failed with some error that suggests we should not continue
     // processing another request at this time.
     LOADING_FAILED_NO_NEXT = 11,
+    // The RequestCoordinator tried to start loading the request but the
+    // loading request was not accepted.
+    LOADING_NOT_ACCEPTED = 12,
+    // The RequestCoordinator did not start loading the request because
+    // updating the status in the request queue failed.
+    QUEUE_UPDATE_FAILED = 13,
     // NOTE: insert new values above this line and update histogram enum too.
     STATUS_COUNT
   };
 
   // Reports the completion status of a request.
   // TODO(dougarnett): consider passing back a request id instead of request.
   typedef base::Callback<void(const SavePageRequest&, RequestStatus)>
       CompletionCallback;
 
   Offliner() {}
   virtual ~Offliner() {}
 
   // Processes |request| to load and save an offline page.
   // Returns whether the request was accepted or not. |callback| is guaranteed
   // to be called if the request was accepted and |Cancel()| is not called.
   virtual bool LoadAndSave(const SavePageRequest& request,
                            const CompletionCallback& callback) = 0;
 
   // Clears the currently processing request, if any, and skips running its
   // CompletionCallback.
   virtual void Cancel() = 0;
 
   // TODO(dougarnett): add policy support methods.
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_BACKGROUND_OFFLINER_H_