Add histograms that track how long it takes to open the new tab page.

chrome/browser/resources/new_new_tab.html

Index: chrome/browser/resources/new_new_tab.html
diff --git a/chrome/browser/resources/new_new_tab.html b/chrome/browser/resources/new_new_tab.html
index f16df88798d4a7de1cdc22ef854c12dc94730f8f..08c452acd2596addc93f1ffd1b044304f6a1e536 100644
--- a/chrome/browser/resources/new_new_tab.html
+++ b/chrome/browser/resources/new_new_tab.html
@@ -13,9 +13,13 @@
 <script>
 // Logging info for benchmarking purposes.
 var log = [];
-function logEvent(name) {
+function logEvent(name, shouldLogTime) {
+  if (shouldLogTime) {
+    chrome.send('logEventTime', [name]);
+  }
   log.push([name, Date.now()]);
 }
+logEvent('NewTab.ScriptStart', true);
 
 var global = this;
 
@@ -50,8 +54,6 @@ registerCallback('recentlyClosedTabs');
 registerCallback('syncMessageChanged');
 registerCallback('tips');
 
-logEvent('log start');
-
 </script>
 <link rel="stylesheet" href="new_new_tab.css">
 <script>