Add voicemail builder method for updating/syncing.

The id of the voicemail is necessary to update a voicemail in the
database and the source data (or unique remote identifier for the
voicemail) is necessary for syncing remotely. Whenever performing a sync
either of data to the server or vise versa, create a voicemail object
using this new method.

Bug: 19236241
Change-Id: Ibc1fd8c1922be13605987d9a3dcd327c438951c8
diff --git a/telecomm/java/android/telecom/Voicemail.java b/telecomm/java/android/telecom/Voicemail.java
index 864c6b1..a884c5f 100644
--- a/telecomm/java/android/telecom/Voicemail.java
+++ b/telecomm/java/android/telecom/Voicemail.java
@@ -57,6 +57,16 @@
     }
 
     /**
+     * Create a {@link Builder} for a {@link Voicemail} to be updated (or deleted).
+     * <p>
+     * The id and source data fields are mandatory for update - id is necessary for updating the
+     * database and source data is necessary for updating the server.
+     */
+    public static Builder createForUpdate(long id, String sourceData) {
+        return new Builder().setId(id).setSourceData(sourceData);
+    }
+
+    /**
      * Builder pattern for creating a {@link Voicemail}. The builder must be created with the
      * {@link #createForInsertion(long, String)} method.
      * <p>