Call waiting support USSD function

-Add USSD function
-Call waiting uses TelephonyManager's get/set methods
Bug: 180540626
Test: build pass. Manual test: set/get call waiting.

Change-Id: Ia03fd4ddef1defb1f0f9091c58ab0f1e43936457
Merged-In: Ia03fd4ddef1defb1f0f9091c58ab0f1e43936457
diff --git a/src/com/android/phone/CarrierXmlParser.java b/src/com/android/phone/CarrierXmlParser.java
index 18602c9..6e01b43 100644
--- a/src/com/android/phone/CarrierXmlParser.java
+++ b/src/com/android/phone/CarrierXmlParser.java
@@ -67,6 +67,7 @@
 
     // To define feature's item name in xml
     public static final String FEATURE_CALL_FORWARDING = "callforwarding";
+    public static final String FEATURE_CALL_WAITING = "callwaiting";
     public static final String FEATURE_CALLER_ID = "callerid";
 
     // COMMAND_NAME is xml's command name.