Require permission for internal broadcast

It was possible for other apps to request removal of the guest user
that was handled by an internal receiver in SystemUI.

Fix requires the broadcast sender to have an internal permission
so that only SystemUI can send that broadcast (PendingIntent).

Bug: 22671268
Change-Id: I63a8ced692e6d1cb2872b962ad247a827dbafbc6
diff --git a/packages/SystemUI/AndroidManifest.xml b/packages/SystemUI/AndroidManifest.xml
index fea7f94..bd58366 100644
--- a/packages/SystemUI/AndroidManifest.xml
+++ b/packages/SystemUI/AndroidManifest.xml
@@ -125,6 +125,11 @@
     <!-- Assist -->
     <uses-permission android:name="android.permission.ACCESS_VOICE_INTERACTION_SERVICE" />
 
+    <!-- Self permission for internal broadcasts. -->
+    <permission android:name="com.android.systemui.permission.SELF"
+            android:protectionLevel="signature" />
+    <uses-permission android:name="com.android.systemui.permission.SELF" />
+
     <application
         android:name=".SystemUIApplication"
         android:persistent="true"