predictors: Don't call IsUrlPrefetchable twice.

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 4363b37543195798cefcdd1b1b7892d1fb69c150..2c5b9846244d7a53fc3077facdaef33b8ebadd72 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.h
+++ b/chrome/browser/predictors/resource_prefetch_predictor.h
@@ -265,9 +265,9 @@ class ResourcePrefetchPredictor
                                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|.