Fall-through for ActionModes with ToolbarActionBar

When using ToolbarActionBar simply fall through to the default window
decor behavior for showing action modes.

Bug 16660506

Change-Id: Ib90282287b2af48f39f9d9ace296581565431eed
diff --git a/core/java/com/android/internal/app/ToolbarActionBar.java b/core/java/com/android/internal/app/ToolbarActionBar.java
index 298dd44..96d7192 100644
--- a/core/java/com/android/internal/app/ToolbarActionBar.java
+++ b/core/java/com/android/internal/app/ToolbarActionBar.java
@@ -179,7 +179,7 @@
 
     @Override
     public ActionMode startActionMode(ActionMode.Callback callback) {
-        return mToolbar.startActionMode(callback);
+        return null;
     }
 
     @Override