Show overlay displaying the state of all sticky keys when it is enabled.

ash/ash_strings.grd

Index: ash/ash_strings.grd
diff --git a/ash/ash_strings.grd b/ash/ash_strings.grd
index c51d8824b5249b079fd005d501931ce042559101..dfab16423416e177cd13be2942c253727518c573 100644
--- a/ash/ash_strings.grd
+++ b/ash/ash_strings.grd
@@ -598,6 +598,18 @@ Press Shift + Alt to switch.
       <message name="IDS_ASH_LOGOUT_CONFIRMATION_BUTTON" desc="The text for okay button of the logout confirmation dialog.">
         Sign out now
       </message>
+      <message name="IDS_ASH_CONTROL_KEY" desc="Name of [Ctrl] key name. Shouldn't be translated in many languages actually. This name should be lower case.">
+        ctrl
+      </message>
+      <message name="IDS_ASH_SHIFT_KEY" desc="Name of [Shift] key. Shouldn't be translated in many languages actually. This name should be lower case.">
+        shift
+      </message>
+      <message name="IDS_ASH_ALT_KEY" desc="Name of [Alt] key name. Shouldn't be translated in many languages actually. This name should be lower case.">
+        alt
+      </message>
+      <message name="IDS_ASH_SEARCH_KEY" desc="Name of [Search] key name. Shouldn't be translated in many languages actually. This name should be lower case.">
+        search
+      </message>
 
       <!-- ChromeOS-specific strings -->
       <if expr="pp_ifdef('chromeos')">