Add phoneAccount->subID conversion method.

Adds method to convert from a phone account to sub ID so that other apps
can use the method instead of implementing the logic themselves.

Change-Id: Icfd8337f7aeca740076afa82db786a905e03ae9c
diff --git a/src/com/android/phone/PhoneInterfaceManager.java b/src/com/android/phone/PhoneInterfaceManager.java
index 9eb0b0b..246c376 100644
--- a/src/com/android/phone/PhoneInterfaceManager.java
+++ b/src/com/android/phone/PhoneInterfaceManager.java
@@ -35,6 +35,7 @@
 import android.os.UserHandle;
 import android.preference.PreferenceManager;
 import android.provider.Settings;
+import android.telecom.PhoneAccount;
 import android.telephony.CellInfo;
 import android.telephony.IccOpenLogicalChannelResponse;
 import android.telephony.NeighboringCellInfo;
@@ -2256,7 +2257,13 @@
      * {@hide}
      * Returns the IMS Registration Status
      */
+    @Override
     public boolean isImsRegistered() {
         return mPhone.isImsRegistered();
     }
+
+    @Override
+    public int getSubIdForPhoneAccount(PhoneAccount phoneAccount) {
+        return PhoneUtils.getSubIdForPhoneAccount(phoneAccount);
+    }
 }