Send UMA stability stats in a separate UMA log on startup.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
===================================================================
--- tools/metrics/histograms/histograms.xml	(revision 240851)
+++ tools/metrics/histograms/histograms.xml	(working copy)
@@ -20326,6 +20326,13 @@
   </summary>
 </histogram>
 
+<histogram name="UMA.LoadLogsTime" units="milliseconds">
+  <summary>
+    The time spent to load (de-serialize) unsent logs from local state, recorded
+    during the MetricsService startup sequence.
+  </summary>
+</histogram>
+
 <histogram name="UMA.LogLoadComplete called">
   <summary>
     Simple counter of the number of times LogLoadComplete was called (bug
@@ -20367,6 +20374,13 @@
   </summary>
 </histogram>
 
+<histogram name="UMA.StoreLogsTime" units="milliseconds">
+  <summary>
+    The time spent to store unsent logs to local state, which is done
+    periodically and also during start up if there was an initial stability log.
+  </summary>
+</histogram>
+
 <histogram name="UMA.Unacceptable_Log_Discarded">
   <obsolete>
     Deprecated as of May, 2012 (i.e. Chrome 21+).  Replaced by the