[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.
+    // The RequestCoordinator did not start loading the request.

[Pete Williamson, 2017/01/03 20:22:53]

Should we split this out into a new code?  I'm not sure if it will be important
to be able to tell the difference between the new and old meaning of the code
while looking at UMA.  Maybe this isn't important, if we can slice the UMA by
milestone, but I thought I'd check to make sure we had a story.

[dougarnett, 2017/01/04 22:23:43]

Done

     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,
     // 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_