[Most Visited] Only log impression metrics on initial NTP load.

chrome/browser/android/most_visited_sites.h

 // Copyright 2013 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_ANDROID_MOST_VISITED_SITES_H_
 #define CHROME_BROWSER_ANDROID_MOST_VISITED_SITES_H_
 
 #include <jni.h>
 
 #include "base/android/scoped_java_ref.h"
@@ skipping 94 matching lines @@
 
   // The observer to be notified when the list of most visited sites changes.
   base::android::ScopedJavaGlobalRef<jobject> observer_;
 
   // The maximum number of most visited sites to return.
   int num_sites_;
 
   // Whether the user is in a control group for the purposes of logging.
   bool is_control_group_;
 
+  // Keeps track of whether the initial NTP load has been done.
+  bool initial_load_done_;
+
   // Counters for UMA metrics.
 
   // Number of tiles using a local thumbnail image for this NTP session.
   int num_local_thumbs_;
   // Number of tiles for which a server thumbnail is provided.
   int num_server_thumbs_;
   // Number of tiles for which no thumbnail is found/specified and a gray tile
   // is used as the main tile.
   int num_empty_thumbs_;
 
   // Copy of the server suggestions (if enabled). Used for logging.
   suggestions::SuggestionsProfile server_suggestions_;
 
   content::NotificationRegistrar registrar_;
 
   MostVisitedSource mv_source_;
 
   // For callbacks may be run after destruction.
   base::WeakPtrFactory<MostVisitedSites> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MostVisitedSites);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_MOST_VISITED_SITES_H_