SimpleCache: more histograms watching how index is loaded.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index a5ac893fa30a308d8b973c252b0bed2092235622..dd6a6f4c20643896a4863ee41281aaeade8d3d51 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9273,6 +9273,17 @@ other types of suffix sets.
   <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.</summary>

[jar (doing other things), 2013/06/05 18:17:54]

Please indicate when this sample is taken.   Is this a hash table, and this
happens when we try to look for a single resource??

[pasko, 2013/06/05 18:35:23]

Done. It happens on index start.

+</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