Adds a new UMA histogram to measure the NTP load time since navigation

chrome/browser/ui/search/search_tab_helper.cc

Index: chrome/browser/ui/search/search_tab_helper.cc
diff --git a/chrome/browser/ui/search/search_tab_helper.cc b/chrome/browser/ui/search/search_tab_helper.cc
index a7a6d5822bda8c9bf2d2e206f71576ce8f1ea80d..ec5f66505f54399bc623a0deb614f7b06127dfd8 100644
--- a/chrome/browser/ui/search/search_tab_helper.cc
+++ b/chrome/browser/ui/search/search_tab_helper.cc
@@ -26,6 +26,7 @@
 #include "chrome/browser/ui/omnibox/omnibox_popup_model.h"
 #include "chrome/browser/ui/omnibox/omnibox_view.h"
 #include "chrome/browser/ui/search/instant_search_prerenderer.h"
+#include "chrome/browser/ui/search/instant_tab.h"
 #include "chrome/browser/ui/search/search_ipc_router_policy_impl.h"
 #include "chrome/browser/ui/search/search_tab_helper_delegate.h"
 #include "chrome/browser/ui/tab_contents/core_tab_helper.h"
@@ -401,6 +402,9 @@ void SearchTabHelper::ThemeInfoChanged(const ThemeBackgroundInfo& theme_info) {
 
 void SearchTabHelper::MostVisitedItemsChanged(
     const std::vector<InstantMostVisitedItem>& items) {
+  // When most visited change, the NTP usually reloads the tiles. This means
+  // our metrics get inconsistent. So we'd rather emit stats now.
+  InstantTab::EmitNtpStatistics(web_contents_);
   ipc_router_.SendMostVisitedItems(items);
 }