Implements the dialog view for logout button tray in public sessions.

ash/ash_strings.grd

Index: ash/ash_strings.grd
diff --git a/ash/ash_strings.grd b/ash/ash_strings.grd
index 75559f4b8445c6493a2d1bee687a6bdf6a12801d..56c573e3387a3f526ec26aa1b5dfd58df75f46cd 100644
--- a/ash/ash_strings.grd
+++ b/ash/ash_strings.grd
@@ -582,6 +582,19 @@ Press Shift + Alt to switch.
         Press Control Shift Q twice to quit.
       </message>
 
+      <message name="IDS_ASH_LOGOUT_CONFIRMATION_TITLE" desc="Dialog title for the logout confirmation dialog.">
+        Exiting Session
+      </message>
+      <message name="IDS_ASH_LOGOUT_CONFIRMATION_WARNING" desc="The text for the logout confirmation dialog.">
+        You will automatically be signed out in <ph name="LOGOUT_TIME_LEFT">$1<ex>5 seconds</ex></ph>.
+      </message>
+      <message name="IDS_ASH_LOGOUT_CONFIRMATION_WARNING_NOW" desc="The text for the logout confirmation dialog with no time left.">
+        You will be signed out now.
+      </message>
+      <message name="IDS_ASH_LOGOUT_CONFIRMATION_BUTTON" desc="The text for okay button of the logout confirmation dialog.">
+        Sign out now
+      </message>
+
       <!-- ChromeOS-specific strings -->
       <if expr="pp_ifdef('chromeos')">
         <part file="ash_chromeos_strings.grdp" />