Adds UMA for PrerenderingOffliner request processing result status.

chrome/browser/android/offline_pages/prerendering_offliner.cc

Index: chrome/browser/android/offline_pages/prerendering_offliner.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_offliner.cc b/chrome/browser/android/offline_pages/prerendering_offliner.cc
index bab7d7fa6630b0794ed865cdf39d5ae6b0a2ed02..7cad8e4a74676697be4c90afe5fca286157f82af 100644
--- a/chrome/browser/android/offline_pages/prerendering_offliner.cc
+++ b/chrome/browser/android/offline_pages/prerendering_offliner.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/android/offline_pages/prerendering_offliner.h"
 
 #include "base/bind.h"
+#include "base/metrics/histogram_macros.h"
 #include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
 #include "components/offline_pages/background/save_page_request.h"
 #include "components/offline_pages/offline_page_model.h"
@@ -13,6 +14,17 @@
 
 namespace offline_pages {
 
+namespace {
+
+void RecordStatusUma(Offliner::RequestStatus request_status) {

[jianli, 2016/06/29 20:47:34]

nit: RecordStatusUMA

+  UMA_HISTOGRAM_ENUMERATION(
+      "OfflinePages.Background.OfflinerStatus",
+      static_cast<int>(request_status),
+      static_cast<int>(Offliner::RequestStatus::STATUS_COUNT));

[Pete Williamson, 2016/06/30 17:20:47]

Will this succeed without static_cast?

[dougarnett, 2016/06/30 18:09:15]

Done.

+}
+
+}  // namespace
+
 PrerenderingOffliner::PrerenderingOffliner(
     content::BrowserContext* browser_context,
     const OfflinerPolicy* policy,
@@ -66,6 +78,7 @@ void PrerenderingOffliner::OnLoadPageDone(
   } else {
     // Clear pending request and then run the completion callback.
     pending_request_.reset(nullptr);
+    RecordStatusUma(load_status);
     completion_callback.Run(request, load_status);
   }
 }
@@ -97,8 +110,9 @@ void PrerenderingOffliner::OnSavePageDone(
   } else {
     // TODO(dougarnett): Consider reflecting some recommendation to retry the
     // request based on specific save error cases.
-    save_status = RequestStatus::FAILED_SAVE;
+    save_status = RequestStatus::SAVE_FAILED;
   }
+  RecordStatusUma(save_status);
   completion_callback.Run(request, save_status);
 }
 
@@ -138,6 +152,7 @@ void PrerenderingOffliner::Cancel() {
     pending_request_.reset(nullptr);
     GetOrCreateLoader()->StopLoading();
     // TODO(dougarnett): Consider ability to cancel SavePage request.
+    RecordStatusUma(Offliner::RequestStatus::REQUEST_CANCELED);
   }
 }