[EasyUnlock] Add a histogram measuring the state of the remote device's lock screen.

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 b18ee6ec230c578381352c4f4ca3c5ece056728c..766c070f198a2e4ab1c117c05c73beb042b67da5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5716,6 +5716,21 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="EasyUnlock.RemoteLockScreenState"
+    enum="EasyUnlockRemoteLockScreenState">
+  <owner>joshwoodward@google.com</owner>
+  <owner>tengs@chromium.org</owner>
+  <owner>isherman@chromium.org</owner>
+  <summary>
+    Whether a lock screen and a trust agent are enabled on the remote device
+    (Android phone) for Easy Unlock. Recorded once per status update message
+    from the remote device. A status update message is expected to be sent once
+    when the secure channel between the local and the remote device is
+    established, and also each time the user-presence status changes on the
+    remote side.

[jwd, 2014/08/14 15:06:15]

Can these messages occur at any time? Or will this only be done when on a
ChromeOS lock screen as the bug implies?

If it's on the lock screen, how will this interact with the metics concept of
idleness?

[Ilya Sherman, 2014/08/14 20:32:50]

The bug is out of date; these messages can occur at any time.  I should have
mentioned when I sent out this review: The CL that landed implemented metrics is
[ http://cr/73251993 ].

+  </summary>
+</histogram>
+
 <histogram name="EasyUnlock.SetupStateOnClose" enum="EasyUnlockSetupState">
   <owner>joshwoodward@google.com</owner>
   <owner>tbarzic@chromium.org</owner>
@@ -38675,6 +38690,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="3" label="Try out notification clicked"/>
 </enum>
 
+<enum name="EasyUnlockRemoteLockScreenState" type="int">
+  <int value="0" label="Unknown state"/>
+  <int value="1" label="Lock screen disabled, trust agent unsupported"/>
+  <int value="2" label="Lock screen disabled, trust agent disabled"/>
+  <int value="3" label="Lock screen disabled, trust agent enabled"/>
+  <int value="4" label="Lock screen enabled, trust agent unsupported"/>
+  <int value="5" label="Lock screen enabled, trust agent disabled"/>
+  <int value="6" label="Lock screen enabled, trust agent enabled"/>
+</enum>
+
 <enum name="EasyUnlockSetupState" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Scan (initial)"/>