Add Connection Event for wifi handover failures.

Adding a new connection event which Telephony can use to inform upper
layers of a failure to handover to WIFI.

Bug: 30697460
Change-Id: I75da2f956a6b70a9bf4cf7128f29968e08172dc3
diff --git a/telephony/java/android/telephony/TelephonyManager.java b/telephony/java/android/telephony/TelephonyManager.java
index a3dc343..ea4ea14 100644
--- a/telephony/java/android/telephony/TelephonyManager.java
+++ b/telephony/java/android/telephony/TelephonyManager.java
@@ -705,6 +705,17 @@
             "android.telephony.extra.LAUNCH_VOICEMAIL_SETTINGS_INTENT";
 
     /**
+     * {@link android.telecom.Connection} event used to indicate that an IMS call failed to be
+     * handed over from LTE to WIFI.
+     * <p>
+     * Sent via {@link android.telecom.Connection#sendConnectionEvent(String, Bundle)}.
+     * The {@link Bundle} parameter is expected to be null when this connection event is used.
+     * @hide
+     */
+    public static final String EVENT_HANDOVER_TO_WIFI_FAILED =
+            "android.telephony.event.EVENT_HANDOVER_TO_WIFI_FAILED";
+
+    /**
      * Response codes for sim activation. Activation completed successfully.
      * @hide
      */