cros: Add enterprise user session metrics

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 47f4d39d47ace9034bb182298b35e380f1b64186..aa096bf96c4c4c6276fcf2043739438366fa90a1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14147,6 +14147,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Enterprise.PublicSession.SessionLength" units="minutes">
+  <owner>xiyuan@chromium.org</owner>
+  <owner>sduraisamy@chromium.org</owner>
+  <summary>Length of a public session.</summary>

[Ilya Sherman, 2017/02/15 00:16:57]

Please clarify exactly what is measured here -- what are the start and stop
events for a public session?  Note that this metric might be hard to interpret,
depending on how long a typical session length is.  For example, during a
30-minute span, I could either have six 5-minute sessions, or one 30-minute
session.

[xiyuan, 2017/02/15 19:08:10]

Done. Let me know if it looks good now.

+</histogram>
+
+<histogram name="Enterprise.RegularUserSession.SessionLength" units="minutes">

[Ilya Sherman, 2017/02/15 00:16:57]

In the C++ code, this is "RegularSession" rather than "RegularUserSession"

[xiyuan, 2017/02/15 19:08:10]

Good catch. Fixed C++ code to use RegularUserSession.

+  <owner>xiyuan@chromium.org</owner>
+  <owner>sduraisamy@chromium.org</owner>
+  <summary>Length of a regular user session on an enrolled device.</summary>

[Ilya Sherman, 2017/02/15 00:16:57]

Ditto

[xiyuan, 2017/02/15 19:08:10]

Done.

+</histogram>
+
 <histogram name="Enterprise.SystemLogPIILeak" enum="SystemLogPIIType">
   <obsolete>
     Deprecated and removed from code as of 01/2016.
@@ -14264,6 +14276,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Enterprise.UserSession.Logins"
+    enum="EnterpriseUserSessionLogins">
+  <owner>xiyuan@chromium.org</owner>
+  <owner>sduraisamy@chromium.org</owner>
+  <summary>Tracks the sign-in events on an enrolled device.</summary>
+</histogram>
+
 <histogram name="Enterprise.UserSigninChoice" enum="SigninChoice">
   <owner>atwilson@chromium.org</owner>
   <summary>
@@ -86872,6 +86891,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="11" label="Request interrupted"/>
 </enum>
 
+<enum name="EnterpriseUserSessionLogins" type="int">
+  <summary>
+    Types of sign-in events as defined in
+    chrome/browser/chromeos/login/enterprise_user_session_metrics.h
+  </summary>
+  <int value="0" label="Regular user"/>
+  <int value="1" label="Manual public session"/>
+  <int value="2" label="Automatic public session"/>
+  <int value="3" label="Manual kiosk session"/>
+  <int value="4" label="Automatic kiosk session"/>
+</enum>
+
 <enum name="ErrorCodesGetAdaptersAddresses" type="int">
   <int value="8" label="ERROR_NOT_ENOUGH_MEMORY"/>
   <int value="87" label="ERROR_INVALID_PARAMETER"/>