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

components/offline_pages/core/background/request_coordinator_event_logger.cc

Index: components/offline_pages/core/background/request_coordinator_event_logger.cc
diff --git a/components/offline_pages/core/background/request_coordinator_event_logger.cc b/components/offline_pages/core/background/request_coordinator_event_logger.cc
index 834f090f661b6ad8918f6d94bebbe18d2c1b53ed..a2d30a2d5ebffd27aa40fcd6a80daa3f18e413ab 100644
--- a/components/offline_pages/core/background/request_coordinator_event_logger.cc
+++ b/components/offline_pages/core/background/request_coordinator_event_logger.cc
@@ -35,6 +35,8 @@ static std::string OfflinerRequestStatusToString(
       return "LOADING_FAILED_NO_RETRY";
     case Offliner::LOADING_FAILED_NO_NEXT:
       return "LOADING_FAILED_NO_NEXT";
+    case Offliner::LOADING_NOT_ACCEPTED:

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

Do we need a new test case?  I noticed that we removed some tests, but I didn't
see any new ones.

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

I removed CanPrerender() method and so removed tests related to that method for
PrerenderingLoader and PrerenderAdapter. 

The existing case of Offliner returning false has different status now
(LOADING_NOT_STARTED => LOADING_NOT_ACCEPTED). There is a test that covers that
(StartScheduledProcessingWithLoadingDisabled) - it used to trigger on the
CanPrerender() check but now the primary code falls through to the LoadAndSave()
call returning false so I think this is ok. 

But there is a remaining case of a database failure for
RequestQueue::MarkAttemptStarted() that could result in LOADING_NOT_STAR
TED or now QUEUE_UPDATE_FAILED. It would be good to have a test for that case
but is a bit off target for this CL and may need some RequestQueue Stub support.
Should I add in a follow up CL?

[Pete Williamson, 2017/01/04 22:31:41]

I'm happy to see the test case in a follow up CL.  Please add either a TODO here
or open a bug.

[dougarnett, 2017/01/04 23:04:58]

TODO-ed

+      return "LOADING_NOT_ACCEPTED";
     default:
       NOTREACHED();
       return std::to_string(static_cast<int>(request_status));