Add action for when the More button is shown in sign in confirmation

BUG=627675,627872

Review-Url: https://codereview.chromium.org/2159393003
Cr-Commit-Position: refs/heads/master@{#407110}

tools/metrics/actions/actions.xml

@@ -13520,6 +13520,14 @@ should be able to be added at any place in this file.
   <obsolete>Removed from codebase.</obsolete>
 </action>
 
+<action name="Signin_MoreButton_Shown">
+  <owner>gogerald@chromium.org</owner>
+  <owner>bzanotti@chromium.org</owner>
+  <description>
+    Recorded when the More button is shown on the sign in confirmation screen.
+  </description>
+</action>
+
 <action name="Signin_Show_EnterpriseAccountPrompt">
   <owner>gogerald@chromium.org</owner>
   <description>