Use different asset when docked stack exists

- Add the ability to add a listener when the existence of the
docked stack changes.
- Register SystemUI as such a listener and switch the recents
button asset when docked stack exists.

Change-Id: I05350878c5adc7ad9f0399f0c42d8d1615d44d02
diff --git a/Android.mk b/Android.mk
index aff6cf2..c1c74ea 100644
--- a/Android.mk
+++ b/Android.mk
@@ -261,7 +261,7 @@
 	core/java/android/view/IApplicationToken.aidl \
 	core/java/android/view/IAppTransitionAnimationSpecsFuture.aidl \
 	core/java/android/view/IAssetAtlas.aidl \
-	core/java/android/view/IDockDividerVisibilityListener.aidl \
+	core/java/android/view/IDockedStackListener.aidl \
 	core/java/android/view/IGraphicsStats.aidl \
 	core/java/android/view/IInputFilter.aidl \
 	core/java/android/view/IInputFilterHost.aidl \