[Offline pages] Resetting offline page metadata store if initial load fails

components/offline_pages/offline_store_types.h

Index: components/offline_pages/offline_store_types.h
diff --git a/components/offline_pages/offline_store_types.h b/components/offline_pages/offline_store_types.h
index 37c701c203a163619d44cf18365414ecadb9d15f..03ce51c9b4ba070f6d717c70d1bf48ab9a3085ab 100644
--- a/components/offline_pages/offline_store_types.h
+++ b/components/offline_pages/offline_store_types.h
@@ -18,11 +18,18 @@ namespace offline_pages {
 // TODO(fgorski): This enum is meant to replace |LoadStatus|.
 // Current store state. When LOADED, the store is operational. When
 // loading or reset fails, it is reflected appropriately.
+// This enum is used in an UMA histogram. Hence the entries here shouldn't
+// be deleted or re-ordered and new ones should be added to the end.
 enum class StoreState {
-  NOT_LOADED,      // Store is not loaded yet.
-  LOADED,          // Store is properly loaded and operational.
-  FAILED_LOADING,  // Store initialization failed.
-  FAILED_RESET,    // Resetting the store failed.
+  NOT_LOADED,        // Store is not loaded yet.

[Mark P, 2016/10/12 16:04:13]

minor nit: put = 0, =1, etc. to help further emphasize that the actual values
are important.

[fgorski, 2016/10/12 20:44:09]

done. Is that a new requirement? I don't remember being asked that before.

[Mark P, 2016/10/12 22:12:15]

It's not a requirement, but it is a good practice.  We haven't been consistent
about asking people to do this, which is why you may have not seen anyone
mention it before.

+  LOADED,            // Store is properly loaded and operational.
+  FAILED_LOADING,    // Store initialization failed.
+  FAILED_RESET,      // Resetting the store failed.
+  FAILED_OPERATION,  // Store is still loaded, but individual operation
+                     // experienced problems. (We want to get UMA if that ever
+                     // happens.
+  // NOTE: always keep this entry at the end.
+  STORE_STATE_COUNT,  // Number of values for UMA reporting.
 };
 
 // Statuses referring to actions taken on items in the stores.