Adds the MostVisitedAction stat. This stat will provide a baseline to compare

chrome/browser/resources/ntp4/most_visited_page.js

Index: chrome/browser/resources/ntp4/most_visited_page.js
===================================================================
--- chrome/browser/resources/ntp4/most_visited_page.js	(revision 134120)
+++ chrome/browser/resources/ntp4/most_visited_page.js	(working copy)
@@ -141,6 +141,8 @@
         // Records the index of this tile.
         chrome.send('metricsHandler:recordInHistogram',
                     ['NewTabPage.MostVisited', this.index, 8]);
+        chrome.send('mostVisitedAction',
+                    [ntp.NtpFollowAction.CLICKED_TILE]);
       }
     },
 
@@ -289,6 +291,9 @@
       this.classList.add('most-visited-page');
       this.data_ = null;
       this.mostVisitedTiles_ = this.getElementsByClassName('most-visited real');
+
+      this.addEventListener('carddeselected', this.handleCardDeselected_);
+      this.addEventListener('cardselected', this.handleCardSelected_);
     },
 
     /**
@@ -317,6 +322,28 @@
     },
 
     /**
+     * Handles the 'card deselected' event (i.e. the user clicked to another
+     * pane).
+     * @param {Event} e The CardChanged event.
+     */
+    handleCardDeselected_: function(e) {
+      if (!document.documentElement.classList.contains('starting-up')) {
+        chrome.send('mostVisitedAction',
+                    [ntp.NtpFollowAction.CLICKED_OTHER_NTP_PANE]);
+      }
+    },
+
+    /**
+     * Handles the 'card selected' event (i.e. the user clicked to select the
+     * Most Visited pane).
+     * @param {Event} e The CardChanged event.
+     */
+    handleCardSelected_: function(e) {
+      if (!document.documentElement.classList.contains('starting-up'))
+        chrome.send('mostVisitedSelected');
+    },
+
+    /**
      * Array of most visited data objects.
      * @type {Array}
      */
@@ -348,6 +375,20 @@
   };
 
   /**
+   * Executed once the NTP has loaded. Checks if the Most Visited pane is
+   * shown or not. If it is shown, the 'mostVisitedSelected' message is sent
+   * to the C++ code, to record the fact that the user has seen this pane.
+   */
+  MostVisitedPage.onLoaded = function() {
+    if (ntp.getCardSlider() &&
+        ntp.getCardSlider().currentCardValue &&
+        ntp.getCardSlider().currentCardValue.classList
+        .contains('most-visited-page')) {
+      chrome.send('mostVisitedSelected');
+    }
+  }
+
+  /**
    * We've gotten additional Most Visited data. Update our old data with the
    * new data. The ordering of the new data is not important, except when a
    * page is pinned. Thus we try to minimize re-ordering.
@@ -424,3 +465,5 @@
     refreshData: refreshData,
   };
 });
+
+document.addEventListener('ntpLoaded', ntp.MostVisitedPage.onLoaded);