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

components/offline_pages/core/background/offliner.h

Index: components/offline_pages/core/background/offliner.h
diff --git a/components/offline_pages/core/background/offliner.h b/components/offline_pages/core/background/offliner.h
index a0159de5bc3169fe9704ad02f1ef8d16984f1979..775e835bca27089f425de53c2daab4648fe60205 100644
--- a/components/offline_pages/core/background/offliner.h
+++ b/components/offline_pages/core/background/offliner.h
@@ -40,13 +40,16 @@ class Offliner {
     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
   };