NTP: Fix metrics recording race condition

components/ntp_tiles/most_visited_sites.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_tiles/most_visited_sites.h"
 
 #include <algorithm>
 #include <set>
 #include <utility>
 
@@ skipping 229 matching lines @@
   }
 
   UMA_HISTOGRAM_SPARSE_SLOWLY("NewTabPage.IconsReal",
                               counts_per_type[ICON_REAL]);
   UMA_HISTOGRAM_SPARSE_SLOWLY("NewTabPage.IconsColor",
                               counts_per_type[ICON_COLOR]);
   UMA_HISTOGRAM_SPARSE_SLOWLY("NewTabPage.IconsGray",
                               counts_per_type[ICON_DEFAULT]);
 }
 
-void MostVisitedSites::RecordOpenedMostVisitedItem(int index, int tile_type) {
-  // TODO(treib): |current_suggestions_| could be updated before this function
-  // is called, leading to DCHECKs and/or memory corruption.  Adjust this
-  // function to work with asynchronous UI.
-  DCHECK_GE(index, 0);
-  DCHECK_LT(index, static_cast<int>(current_suggestions_.size()));
-
+void MostVisitedSites::RecordOpenedMostVisitedItem(int index,
+                                                   int tile_type,
+                                                   int source) {
   UMA_HISTOGRAM_ENUMERATION("NewTabPage.MostVisited", index, num_sites_);
 
   std::string histogram = base::StringPrintf(
-      "NewTabPage.MostVisited.%s",
-      GetSourceHistogramName(current_suggestions_[index].source).c_str());
+      "NewTabPage.MostVisited.%s", GetSourceHistogramName(source).c_str());
   LogHistogramEvent(histogram, index, num_sites_);
 
-  histogram = base::StringPrintf(
-      "NewTabPage.TileTypeClicked.%s",
-      GetSourceHistogramName(current_suggestions_[index].source).c_str());
+  histogram = base::StringPrintf("NewTabPage.TileTypeClicked.%s",
+                                 GetSourceHistogramName(source).c_str());
   LogHistogramEvent(histogram, tile_type, NUM_TILE_TYPES);
 }
 
 void MostVisitedSites::OnBlockedSitesChanged() {
   BuildCurrentSuggestions();
 }
 
 // static
 void MostVisitedSites::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
@@ skipping 272 matching lines @@
 
 void MostVisitedSites::TopSitesChanged(TopSites* top_sites,
                                        ChangeReason change_reason) {
   if (mv_source_ == TOP_SITES) {
     // The displayed suggestions are invalidated.
     InitiateTopSitesQuery();
   }
 }
 
 }  // namespace ntp_tiles