Record impressions/navigations only once per tile.

chrome/browser/ui/webui/ntp/ntp_user_data_logger.h

Index: chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
diff --git a/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h b/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
index 6e6f965b058ad9fab999be97fa0a462f5c26fb1a..13ed126232772df57fe7e6bdafd87ee3f19d13aa 100644
--- a/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
+++ b/chrome/browser/ui/webui/ntp/ntp_user_data_logger.h
@@ -25,6 +25,9 @@ class NTPUserDataLogger
  public:
   ~NTPUserDataLogger() override;
 
+  // Gets the associated NTPUserDataLogger, creating it if necessary.
+  //
+  // MUST be called only when the NTP is active.

[Marc Treib, 2016/07/12 08:17:46]

Can we DCHECK this? search::IsInstantNTP might be the right thing.

[sfiera, 2016/07/14 14:11:08]

DCHECK added.

   static NTPUserDataLogger* GetOrCreateFromWebContents(
       content::WebContents* content);
 
@@ -42,9 +45,6 @@ class NTPUserDataLogger
   // Called when the tab is closed. Logs statistics.
   void TabDeactivated();
 
-  // Called when the set of most visited sites changes. Flushes statistics.
-  void MostVisitedItemsChanged();
-
  protected:
   explicit NTPUserDataLogger(content::WebContents* contents);
 
@@ -63,16 +63,26 @@ class NTPUserDataLogger
       const content::LoadCommittedDetails& load_details) override;
 
   // To clarify at the call site whether we are calling EmitNtpStatistics() for
-  // a good reason (CLOSED, NAVIGATED_AWAY) or a questionable one (MV_CHANGED,
-  // INTERNAL_FLUSH).
-  // TODO(sfiera): remove MV_CHANGED, INTERNAL_FLUSH.
-  enum class EmitReason { CLOSED, NAVIGATED_AWAY, MV_CHANGED, INTERNAL_FLUSH };
+  // a good reason (CLOSED, NAVIGATED_AWAY) or a questionable one
+  // (INTERNAL_FLUSH).
+  // TODO(sfiera): remove INTERNAL_FLUSH.
+  enum class EmitReason { CLOSED, NAVIGATED_AWAY, INTERNAL_FLUSH };
 
   // Logs a number of statistics regarding the NTP. Called when an NTP tab is
   // about to be deactivated (be it by switching tabs, losing focus or closing
   // the tab/shutting down Chrome), or when the user navigates to a URL.
   void EmitNtpStatistics(EmitReason reason);
 
+  // Records whether we have yet logged an impression for the tile at a given
+  // index. A typical NTP will log 8 impressions, but could record fewer for new
+  // users that haven't built up a history yet.
+  //
+  // If something happens that causes the NTP to pull tiles from different
+  // sources, such as logging in (switching from client to server tiles), then
+  // only the impressions for the first source will be logged, leaving the
+  // number of impressions for a source slightly out-of-sync with navigations.
+  std::vector<bool> impression_was_logged_;
+
   // True if at least one iframe came from a server-side suggestion.
   bool has_server_side_suggestions_;