Allow custom keyguard "prompt reason"

Adds the possibility of presenting a custom message on
the keyboard if you're trying to dismiss the keyguard.

This is particularly useful when you're showing the
bouncer because custom authentication (SmarLock)
failed.

Test: launch FLAG_SHOW_WHEN_LOCKED activity and
      call KeyguardManager#requestDismissKeyguard
Fixes: 63940122
Change-Id: I0d88c0e59521887efa56d74874062b2b14970e4e
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 4bf1cb0..e2642c5 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -3394,6 +3394,12 @@
     <permission android:name="android.permission.PROVIDE_TRUST_AGENT"
         android:protectionLevel="signature|privileged" />
 
+    <!-- @SystemApi Allows an application to show a message
+         on the keyguard when asking to dismiss it.
+         @hide For security reasons, this is a platform-only permission. -->
+    <permission android:name="android.permission.SHOW_KEYGUARD_MESSAGE"
+        android:protectionLevel="signature|privileged" />
+
     <!-- Allows an application to launch the trust agent settings activity.
         @hide -->
     <permission android:name="android.permission.LAUNCH_TRUST_AGENT_SETTINGS"