Implement setNetworkPreferenceForUser.

Test: FrameworksNetTests
Change-Id: I8f18083b5857289892fe8adea5f5ea3f5dbe0809
diff --git a/framework/src/android/net/OemNetworkPreferences.java b/framework/src/android/net/OemNetworkPreferences.java
index 48bd297..5a76cd6 100644
--- a/framework/src/android/net/OemNetworkPreferences.java
+++ b/framework/src/android/net/OemNetworkPreferences.java
@@ -73,6 +73,14 @@
     private final Bundle mNetworkMappings;
 
     /**
+     * Return whether this object is empty.
+     * @hide
+     */
+    public boolean isEmpty() {
+        return mNetworkMappings.keySet().size() == 0;
+    }
+
+    /**
      * Return the currently built application package name to {@link OemNetworkPreference} mappings.
      * @return the current network preferences map.
      */