[NTP4] Track the position of each app that's launched.

chrome/browser/resources/ntp4/apps_page.js

Index: chrome/browser/resources/ntp4/apps_page.js
diff --git a/chrome/browser/resources/ntp4/apps_page.js b/chrome/browser/resources/ntp4/apps_page.js
index 8cbf35c8935756adc73781988fb0f03800d87ce9..93c8e1ab99f630344a322ab31293975405780b5a 100644
--- a/chrome/browser/resources/ntp4/apps_page.js
+++ b/chrome/browser/resources/ntp4/apps_page.js
@@ -475,6 +475,7 @@ cr.define('ntp4', function() {
                                  'utm_source',
                                  'chrome-ntp-icon');
 
+      this.recordAppLaunchedFromIndex_();
       chrome.send('launchApp',
                   [this.appId, APP_LAUNCH.NTP_APPS_MAXIMIZED, url,
                    e.button, e.altKey, e.ctrlKey, e.metaKey, e.shiftKey]);
@@ -490,6 +491,7 @@ cr.define('ntp4', function() {
      */
     onKeydown_: function(e) {
       if (e.keyIdentifier == 'Enter') {
+        this.recordAppLaunchedFromIndex_();
         chrome.send('launchApp',
                     [this.appId, APP_LAUNCH.NTP_APPS_MAXIMIZED, '',
                      0, e.altKey, e.ctrlKey, e.metaKey, e.shiftKey]);
@@ -499,6 +501,16 @@ cr.define('ntp4', function() {
     },
 
     /**
+     * Records the index of an app when launched.
+     * @private
+     */
+    recordAppLaunchedFromIndex_: function() {
+      var page = this.tile.tilePage;
+      var wide = page.layoutValues.numRowTiles == page.gridValues.maxColCount;
+      chrome.send('recordAppLaunchedFromIndex', [this.tile.index, wide]);
+    },
+
+    /**
      * Adds a node to the list of targets that will launch the app. This list
      * is also used in onMousedown to determine whether the app contents should
      * be shown as active (if we don't do this, then clicking anywhere in