[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 9002c9d243f8f0406de8bbc3c054f4c802064d85..457b6bd648d4186f69dc8a2dbbcfb34b95ca4989 100644
--- a/components/offline_pages/offline_store_types.h
+++ b/components/offline_pages/offline_store_types.h
@@ -15,14 +15,20 @@
 // offline page related components.
 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 = 0,        // Store is not loaded yet.
+  LOADED = 1,            // Store is properly loaded and operational.
+  FAILED_LOADING = 2,    // Store initialization failed.
+  FAILED_RESET = 3,      // Resetting the store failed.
+  FAILED_OPERATION = 4,  // 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.