Add key for passing domain compare feature flag to GsmCdmaPhone.

Bug: 263552148
Test: Manual call testing
Change-Id: I524381ca74e60d7103421dafd0b3e9f1b2aed173

telephony/java/com/android/internal/telephony/PhoneConstants.java

@@ -250,6 +250,9 @@ public class PhoneConstants {
      */
     public static final int DOMAIN_NON_3GPP_PS = 4;
 
+    /** Key to enable comparison of domain selection results from legacy and new code. */
+    public static final String EXTRA_COMPARE_DOMAIN = "compare_domain";
+
     /** The key to specify the emergency service category */
     public static final String EXTRA_EMERGENCY_SERVICE_CATEGORY = "emergency_service_category";
 }