predictors: Don't call IsUrlPrefetchable twice.

chrome/browser/predictors/resource_prefetch_predictor.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_H_
 #define CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 247 matching lines @@
   // Sets the |stats_collector| which is used to report histograms.
   void SetStatsCollector(LoadingStatsCollector* stats_collector);
 
   // Returns true iff there is PrefetchData that can be used for a
   // |main_frame_url| and fills |prediction| with resources that need to be
   // prefetched. |prediction| pointer may be nullptr to get return value only.
   virtual bool GetPrefetchData(const GURL& main_frame_url,
                                Prediction* prediction) const;
 
  private:
-  // Starts prefetching if it is enabled and prefetching data exists for the
-  // |main_frame_url| either at the URL or at the host level.
-  void StartPrefetching(const GURL& main_frame_url);
+  // Starts prefetching for |main_frame_url| from a |prediction|.
+  void StartPrefetching(const GURL& main_frame_url,
+                        const Prediction& prediction);
 
   // Stops prefetching that may be in progress corresponding to
   // |main_frame_url|.
   void StopPrefetching(const GURL& main_frame_url);
 
   friend class LoadingPredictor;
   friend class ::PredictorsHandler;
   friend class ResourcePrefetchPredictorTest;
   friend class ResourcePrefetchPredictorBrowserTest;
 
@@ skipping 222 matching lines @@
 
  private:
   ResourcePrefetchPredictor* predictor_;
 
   DISALLOW_COPY_AND_ASSIGN(TestObserver);
 };
 
 }  // namespace predictors
 
 #endif  // CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_H_