Adds UMA for PrerenderingOffliner request processing result status.

components/offline_pages/background/offliner.h

Index: components/offline_pages/background/offliner.h
diff --git a/components/offline_pages/background/offliner.h b/components/offline_pages/background/offliner.h
index 745fc6181b678670a377ce8ecaa41c2b0e22c38d..0429096c26b24efcc00b4334ac31258e045101d0 100644
--- a/components/offline_pages/background/offliner.h
+++ b/components/offline_pages/background/offliner.h
@@ -16,14 +16,18 @@ class SavePageRequest;
 class Offliner {
  public:
   // Status of processing an offline page request.
-  enum class RequestStatus {
-    UNKNOWN,      // No status determined/reported yet.
-    LOADED,       // Page loaded but not (yet) saved.
-    SAVED,        // Offline page snapshot saved.
-    CANCELED,     // Request was canceled.
-    FAILED,       // Failed to load page.
-    FAILED_SAVE,  // Failed to save loaded page.
-    // TODO(dougarnett): Define a retry-able failure status.
+  // NOTE: These values correspond to the
+  // OfflinePagesBackgroundOfflinerRequestStatus histogram enum.

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

Can we make the wording of the comment a bit stronger?
 // WARNING: You must change histograms.xml to add the enum value there too if
you
 // add a new enum value here.

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

Done.

+  enum RequestStatus {
+    UNKNOWN = 0,           // No status determined/reported yet.
+    LOADED = 1,            // Page loaded but not (yet) saved.
+    SAVED = 2,             // Offline page snapshot saved.
+    REQUEST_CANCELED = 3,  // Request was canceled by requester (from above).
+    LOAD_CANCELED = 4,     // Load was canceled vs. failed (from below).
+    LOAD_FAILED = 5,       // Failed to load page.
+    SAVE_FAILED = 6,       // Failed to save loaded page.
+    // NOTE: insert new values above this line and update histogram enum too.
+    STATUS_COUNT
   };
 
   // Reports the completion status of a request.