Add hidden methods to set/get default dialer across users

Bug: 20696062
Change-Id: Ib26197c670caed9f2eab3e252c8fbc6102e0d476
diff --git a/src/com/android/server/telecom/TelecomServiceImpl.java b/src/com/android/server/telecom/TelecomServiceImpl.java
index 6bfef57..f9ee74c 100644
--- a/src/com/android/server/telecom/TelecomServiceImpl.java
+++ b/src/com/android/server/telecom/TelecomServiceImpl.java
@@ -468,7 +468,12 @@
          */
         @Override
         public String getDefaultDialerPackage() {
-            return DefaultDialerManager.getDefaultDialerApplication(mContext);
+            final long token = Binder.clearCallingIdentity();
+            try {
+                return DefaultDialerManager.getDefaultDialerApplication(mContext);
+            } finally {
+                Binder.restoreCallingIdentity(token);
+            }
         }
 
         /**