Add missing UMA definitions about ScreenLocker to histograms.xml

The metrics were added long time ago crrev.com/64367 without
the corresponding changes to histograms.xml. The metrics still
look interesting hence this change is to update histograms.xml.

BUG=643563

Change-Id: I0ea55648b27b938dc5780932ac9dde31f4e1ff09
Reviewed-on: https://chromium-review.googlesource.com/842427
Commit-Queue: Satoru Takabayashi <satorux@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557798}

tools/metrics/histograms/histograms.xml

@@ -81539,6 +81539,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ScreenLocker.AuthenticationFailureTime" units="ms">
+  <owner>sammiequon@chromium.org</owner>
+  <summary>The time spent for authentication in case of a failure.</summary>
+</histogram>
+
 <histogram name="ScreenLocker.AuthenticationSuccess" enum="UnlockType">
   <owner>sammiequon@chromium.org</owner>
   <summary>
@@ -81547,6 +81552,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ScreenLocker.AuthenticationSuccessTime" units="ms">
+  <owner>sammiequon@chromium.org</owner>
+  <summary>The time spent for authentication in case of a success.</summary>
+</histogram>
+
+<histogram name="ScreenLocker.ScreenLockTime" units="ms">
+  <owner>sammiequon@chromium.org</owner>
+  <summary>The time spent before the screen locker is ready.</summary>
+</histogram>
+
 <histogram name="Sdch3.AdvertisedWithSecureScheme" enum="BooleanHttps">
   <obsolete>
     Experiment complete, histogram gathering code removed.