Add "SCHEME_VOICEMAIL" as a constant in CallUtil.

We check for the voicemail scheme in InCallUI so add this constant to
ContactsCommon.

Bug: 17363355
Change-Id: Ieb09f7772654ed738fb5127bb6d9fed1246e3a00
diff --git a/src/com/android/contacts/common/CallUtil.java b/src/com/android/contacts/common/CallUtil.java
index ea53571..307c975 100644
--- a/src/com/android/contacts/common/CallUtil.java
+++ b/src/com/android/contacts/common/CallUtil.java
@@ -36,6 +36,7 @@
     public static final String SCHEME_MAILTO = "mailto";
     public static final String SCHEME_IMTO = "imto";
     public static final String SCHEME_SIP = "sip";
+    public static final String SCHEME_VOICEMAIL = "voicemail";
 
     /**
      * Return an Intent for making a phone call. Scheme (e.g. tel, sip) will be determined