Add EXTRA_HANDOVER_FROM_PHONE_ACCOUNT.

Used in handovers to tell the account we're handing over to which account
the call is from.

Test: Manual
Bug: 38027075
Change-Id: I9b61a5fce3e4f7344174a1b81f4964ca02b71ccd
diff --git a/telecomm/java/android/telecom/TelecomManager.java b/telecomm/java/android/telecom/TelecomManager.java
index 331328d..b1eedf5 100644
--- a/telecomm/java/android/telecom/TelecomManager.java
+++ b/telecomm/java/android/telecom/TelecomManager.java
@@ -369,6 +369,15 @@
     public static final String EXTRA_IS_HANDOVER = "android.telecom.extra.IS_HANDOVER";
 
     /**
+     * Parcelable extra used with {@link #EXTRA_IS_HANDOVER} to indicate the source
+     * {@link PhoneAccountHandle} when initiating a handover which {@link ConnectionService}
+     * the handover is from.
+     * @hide
+     */
+    public static final String EXTRA_HANDOVER_FROM_PHONE_ACCOUNT =
+            "android.telecom.extra.HANDOVER_FROM_PHONE_ACCOUNT";
+
+    /**
      * Extra key specified in the {@link ConnectionRequest#getExtras()} when Telecom calls
      * {@link ConnectionService#onCreateOutgoingConnection(PhoneAccountHandle, ConnectionRequest)}
      * to inform the {@link ConnectionService} what the initial {@link CallAudioState} of the