Adding a destination platform histogram for UMA.

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 93ea14f12ed4a018cc65c2f10994b2c3a7290c46..f247d0e191de79fcef9f196233f21b376186a4be 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1218,7 +1218,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram name="Arc.IntentHandlerAction" enum="ArcIntentHandlerAction">
   <owner>elijahtaylor@google.com</owner>
   <owner>mitsuji@google.com</owner>
-  <summary>Arc intent handler action taken by user.</summary>
+  <summary>
+    ARC intent handler action taken by user. Starting on [M-56] and when the
+    CloseReason equals PREFERRED_ACTIVITY_FOUND we put both navigations going to
+    ARC or Chrome on the same bucket, this is for navigations falling on the
+    &quot;external protocol&quot; category (non http/https).
+  </summary>
+</histogram>
+
+<histogram name="Arc.IntentHandlerDestinationPlatform"
+    enum="ArcIntentHandlerDestinationPlatform">
+  <owner>elijahtaylor@google.com</owner>
+  <owner>mitsuji@google.com</owner>
+  <summary>
+    ARC intent handler destination platform. The destination may be specified
+    due to the user explicit selection or a previously stored preference.
+  </summary>
 </histogram>
 
 <histogram name="Arc.LowMemoryKiller.Count">
@@ -73462,6 +73477,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="4" label="Preferred activity found"/>
 </enum>
 
+<enum name="ArcIntentHandlerDestinationPlatform" type="int">
+  <summary>
+    Defines ARC intent handler platforms to continue the navigation.
+  </summary>
+  <int value="0" label="ARC"/>
+  <int value="1" label="Chrome"/>
+</enum>
+
 <enum name="ArcOptInAction" type="int">
   <summary>Defines Arc OptIn actions</summary>
   <int value="0" label="Opted In"/>