[Smart Lock] Add UMA metrics to measure duration of unlock.

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 f6bf6b5ba08469b0d56fcffee3df4f282993a176..f32714fe863f06d3c8179bc1b78cce5457c6ee20 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6536,6 +6536,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="EasyUnlock.AuthEvent.SignIn.Duration" units="ms">
+  <owner>isherman@google.com</owner>
+  <owner>tengs@google.com</owner>
+  <owner>xiaowenx@google.com</owner>
+  <summary>
+    Measures the time elapsed between the user focusing her user pod and signing
+    in using Smart Lock.
+  </summary>
+</histogram>
+
 <histogram name="EasyUnlock.AuthEvent.Unlock" enum="EasyUnlockAuthEvent">
   <owner>isherman@google.com</owner>
   <owner>xiaowenx@google.com</owner>
@@ -6548,6 +6558,18 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="EasyUnlock.AuthEvent.Unlock.Duration" units="ms">
+  <owner>isherman@google.com</owner>
+  <owner>tengs@google.com</owner>
+  <owner>xiaowenx@google.com</owner>
+  <summary>
+    Measures the time elapsed between the lock screen being shown and the user
+    unlocking the device using Smart Lock. The lock screen is typically shown
+    when the user opens her Chromebook's lid (or otherwise wakes the computer),
+    but can also be shown when the user manually locks the device.
+  </summary>
+</histogram>
+
 <histogram name="EasyUnlock.AuthProximity.RemoteDeviceModelHash"
     enum="EasyUnlockDeviceModelHash">
   <owner>tengs@chromium.org</owner>