Eliminate NOTIFICATION_HISTORY_LOADED notification

chrome/browser/predictors/resource_prefetch_predictor.h

Index: chrome/browser/predictors/resource_prefetch_predictor.h
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.h b/chrome/browser/predictors/resource_prefetch_predictor.h
index c6eb7157c458f932467670b46cdffb12150189f1..7d88b49e08575e2d1958f52408c176efcb176f45 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.h
+++ b/chrome/browser/predictors/resource_prefetch_predictor.h
@@ -13,11 +13,13 @@
 #include "base/memory/linked_ptr.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/scoped_observer.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/time/time.h"
 #include "chrome/browser/predictors/resource_prefetch_common.h"
 #include "chrome/browser/predictors/resource_prefetch_predictor_tables.h"
 #include "chrome/browser/predictors/resource_prefetcher.h"
+#include "components/history/core/browser/history_service_observer.h"
 #include "components/history/core/browser/history_types.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "content/public/browser/notification_observer.h"
@@ -75,6 +77,7 @@ class ResourcePrefetcherManager;
 class ResourcePrefetchPredictor
     : public KeyedService,
       public content::NotificationObserver,
+      public history::HistoryServiceObserver,
       public base::SupportsWeakPtr<ResourcePrefetchPredictor> {
  public:
   // Stores the data that we need to get from the URLRequest.
@@ -126,6 +129,9 @@ class ResourcePrefetchPredictor
       PrefetchKeyType key_type,
       ResourcePrefetcher::RequestVector* requests);
 
+  // history::HistoryServiceObserver:
+  void OnHistoryServiceLoaded(HistoryService* history_service) override;
+
  private:
   friend class ::PredictorsHandler;
   friend class ResourcePrefetchPredictorTest;
@@ -288,6 +294,11 @@ class ResourcePrefetchPredictor
     tables_ = tables;
   }
 
+  // If HistoryService exists and its Backend is loaded,
+  // calls the OnHistoryAndCacheLoaded.
+  // Else wait for the OnHistoryServiceLoaded event.
+  bool CheckForHistoryService();
+
   Profile* const profile_;
   ResourcePrefetchPredictorConfig const config_;
   InitializationState initialization_state_;
@@ -306,6 +317,9 @@ class ResourcePrefetchPredictor
   ResultsMap results_map_;
   STLValueDeleter<ResultsMap> results_map_deleter_;
 
+  ScopedObserver<HistoryService, history::HistoryServiceObserver>
+      history_service_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(ResourcePrefetchPredictor);
 };