Support saving browser metrics to disk and reading them during next run.

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 00088bba08713f682c826cf38baac719d392b403..bae8856e1eabbdecb56c7620e3fded16eab9b5be 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -55570,6 +55570,42 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.FileMetricsProvider.InitialAccessResult"
+    enum="FileMetricsProviderAccessResult">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records attempts to access a file for the purpose of extracting initial
+    stability metrics.
+  </summary>
+</histogram>
+
+<histogram name="UMA.FileMetricsProvider.InitialCheckTime" units="ms">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records how much real time was spent checking and mapping an initial metrics

[Ilya Sherman, 2016/05/05 22:22:52]

nit: s/real/wall (applies throughout)

[bcwhite, 2016/05/06 16:59:27]

Done.

+    file on disk.
+  </summary>
+</histogram>
+
+<histogram name="UMA.FileMetricsProvider.InitialSnapshotTime" units="ms">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records how much real time was spent collecting initial stability metrics
+    from a file on disk.
+  </summary>
+</histogram>
+
+<histogram name="UMA.FileMetricsProvider.SnapshotTime" units="ms">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records how much real time was spent collecting metrics from a file on disk.
+  </summary>
+</histogram>
+
 <histogram name="UMA.GeneratedLowEntropySource" enum="Boolean">
   <obsolete>
     Deprecated as of August 2015. No longer tracked.