[Contextual Search] Add Mojo-enabled API component.

components/contextual_search/common/overlay_page_notifier_service.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module dom_distiller;
+module contextual_search;
 
 // This service is implemented in the renderer process and is used by the
-// browser to notify a renderer that is page is a distiller page.
-interface DistillerPageNotifierService {
-  NotifyIsDistillerPage();
+// browser to notify a renderer that its page is presented in an overlay panel.
+interface OverlayPageNotifierService {
+  NotifyIsContextualSearchOverlay();
 };