SimpleCache: more histograms watching how index is loaded.

tools/metrics/histograms/histograms.xml

 <!--
 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.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 9294 matching lines @@
 </histogram>
 
 <histogram name="SimpleCache.IndexCorrupt" enum="BooleanCorrupt">
   <summary>For each index load, whether the index file was corrupt.</summary>
 </histogram>
 
 <histogram name="SimpleCache.IndexCreatedEntryCount">
   <summary>The number of entries in a newly created index file.</summary>
 </histogram>
 
+<histogram name="SimpleCache.IndexEntriesLoaded">
+  <summary>Number of entries loaded from the index file on start.</summary>
+</histogram>
+
+<histogram name="SimpleCache.IndexEntriesRestored">
+  <summary>
+    Number of entries restored from disk when there was no index or the index
+    was corrupted.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.IndexInitializationWaiters">
   <summary>
     At the time of index initialization, the number of enqueued jobs awaiting
     index initialization.
   </summary>
 </histogram>
 
 <histogram name="SimpleCache.IndexInitializeMethod"
     enum="SimpleCacheIndexInitializeMethod">
   <summary>The method used to initialize the simple cache index.</summary>
@@ skipping 7853 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>