Adding WidgetAddFlowHandler to handle widget addition and configuration.

This will allow us to override the implementation and provide custom
logic for widget addition.

Bug: 33584624
Change-Id: I310bf39e301c7e1c8de4f62456594535e2fe5bbc
diff --git a/src/com/android/launcher3/LauncherAppWidgetInfo.java b/src/com/android/launcher3/LauncherAppWidgetInfo.java
index b68a64b..285a93c 100644
--- a/src/com/android/launcher3/LauncherAppWidgetInfo.java
+++ b/src/com/android/launcher3/LauncherAppWidgetInfo.java
@@ -76,7 +76,7 @@
      * Identifier for this widget when talking with
      * {@link android.appwidget.AppWidgetManager} for updates.
      */
-    int appWidgetId = NO_ID;
+    public int appWidgetId = NO_ID;
 
     public ComponentName providerName;