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..cfbb47e7e02bab49080781dab582fb6520ca806d 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_STICKY_KEY_CONTROL" desc="Name of [Ctrl] key name used for sticky keys. Shouldn't be translated in many languages actually.">

[James Cook, 2014/01/15 22:53:53]

These could probably have more generic names like IDS_ASH_CONTROL_KEY so other
features would be OK with using them.  You might also want to explicitly say
they should be lower-case.

[Tim Song, 2014/01/16 00:01:59]

Done.

+        ctrl
+      </message>
+      <message name="IDS_ASH_STICKY_KEY_SHIFT" desc="Name of [Shift] key name used for sticky keys. Shouldn't be translated in many languages actually.">
+        shift
+      </message>
+      <message name="IDS_ASH_STICKY_KEY_ALT" desc="Name of [Alt] key name used for sticky keys. Shouldn't be translated in many languages actually.">
+        alt
+      </message>
+      <message name="IDS_ASH_STICKY_KEY_SEARCH" desc="Name of [Search] key name used for sticky keys. Shouldn't be translated in many languages actually.">
+        search
+      </message>
 
       <!-- ChromeOS-specific strings -->
       <if expr="pp_ifdef('chromeos')">