Adds UMA for PrerenderingOffliner request processing result status.

components/offline_pages/background/request_coordinator.cc

Index: components/offline_pages/background/request_coordinator.cc
diff --git a/components/offline_pages/background/request_coordinator.cc b/components/offline_pages/background/request_coordinator.cc
index 6292aa8cc7b24ddb6fc7fe430d8529531f288589..c6397b1bbbaab7d7f80ace1b8a3b1a8e3d539f87 100644
--- a/components/offline_pages/background/request_coordinator.cc
+++ b/components/offline_pages/background/request_coordinator.cc
@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 #include "components/offline_pages/background/offliner_factory.h"
 #include "components/offline_pages/background/offliner_policy.h"
@@ -19,6 +20,15 @@
 namespace offline_pages {
 
 namespace {
+
+// Records the final request status UMA for an offlining request. This should
+// only be called once per Offliner::LoadAndSave request.

[fgorski, 2016/07/12 22:17:06]

where is the comment about not reporting loaded or unknown status that we
discussed in comments on patch 1 (next to enum definition)?

Are they going to be reported in the end? Or was it missed?

Perhaps it makes sense to DCHECK as well

[dougarnett, 2016/07/12 23:07:59]

Ok, added comment about the two interim status codes in enum defn and added
DCHECKs in offliner->coordinator callback (as that is more central point for
coordinator not expecting them and also then not reporting them.

+void RecordOfflinerResultUMA(Offliner::RequestStatus request_status) {
+  UMA_HISTOGRAM_ENUMERATION("OfflinePages.Background.OfflinerRequestStatus",
+                            request_status,
+                            Offliner::RequestStatus::STATUS_COUNT);
+}
+
 // TODO(dougarnett/petewil): Move to Policy object. Also consider lower minimum
 // battery percentage once there is some processing time limits in place.
 const Scheduler::TriggerConditions kUserRequestTriggerConditions(
@@ -92,6 +102,11 @@ void RequestCoordinator::StopProcessing() {
   if (offliner_ && is_busy_)
     offliner_->Cancel();
 
+  // Stopping offliner means it will not call callback.
+  last_offlining_status_ =
+      Offliner::RequestStatus::REQUEST_COORDINATOR_CANCELED;
+  RecordOfflinerResultUMA(last_offlining_status_);
+
   // Let the scheduler know we are done processing.
   scheduler_callback_.Run(true);
 }
@@ -172,6 +187,7 @@ void RequestCoordinator::OfflinerDoneCallback(const SavePageRequest& request,
       "Saved",
       request.request_id());
   last_offlining_status_ = status;
+  RecordOfflinerResultUMA(last_offlining_status_);
   watchdog_timer_.Stop();
 
   is_busy_ = false;