Add a histogram for tracking web store promo

chrome/browser/resources/new_new_tab.js

Index: chrome/browser/resources/new_new_tab.js
diff --git a/chrome/browser/resources/new_new_tab.js b/chrome/browser/resources/new_new_tab.js
index 6b3be4ad5560bb9e2ead69d5f11da662574cb817..77bf754c4a47bfa562f460b8a2095a077de817f3 100644
--- a/chrome/browser/resources/new_new_tab.js
+++ b/chrome/browser/resources/new_new_tab.js
@@ -908,6 +908,13 @@ function handleIfEnterKey(f) {
   };
 }
 
+function handleIfMiddleClick(f) {
+  return function(e) {
+    if (e.button == 1)
+      f(e);
+  };
+}
+
 function maybeReopenTab(e) {
   var el = findAncestor(e.target, function(el) {
     return el.sessionId !== undefined;
@@ -1202,12 +1209,20 @@ function isDoneLoading() {
   return !document.body.classList.contains('loading');
 }
 
+function recordWebStoreLaunch() {
+  chrome.send('recordWebStoreLaunch', []);
+}
+
 // Initialize the apps promo.
 document.addEventListener('DOMContentLoaded', function() {
   var promoText1 = $('apps-promo-text1');
   promoText1.innerHTML = promoText1.textContent;
   promoText1.querySelector('a').href = localStrings.getString('web_store_url');
 
+  var promoLink = promoText1.querySelector('a');
+  promoLink.onclick = recordWebStoreLaunch;
+  promoLink.onmousedown = handleIfMiddleClick(recordWebStoreLaunch);
+
   $('apps-promo-hide').addEventListener('click', function() {
     chrome.send('hideAppsPromo', []);
     document.documentElement.classList.remove('apps-promo-visible');