[Contextual Search] Add Mojo-enabled API component.

components/contextual_search/BUILD.gn

+# 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.
+
+if (is_android) {
+  import("//build/config/android/rules.gni")
+}
+
+# GYP: //components/contextual_search:contextual_search
+static_library("contextual_search") {
+  sources = [
+    "contextual_search_api_service_impl.cc",
+    "contextual_search_api_service_impl.h",
+    "contextual_search_wrapper.cc",
+    "contextual_search_wrapper.h",
+    "overlay_js_render_frame_observer.cc",
+    "overlay_js_render_frame_observer.h",
+    "overlay_page_notifier_service_impl.cc",
+    "overlay_page_notifier_service_impl.h",
+  ]
+  deps = [
+    "//base",
+  ]
+}
+
+# GYP version: components/overlay_panel.gypi:overlay_panel_mojo_bindings
+mojom("mojo_bindings") {
+  sources = [
+    "common/contextual_search_api_service.mojom",
+    "common/overlay_page_notifier_service.mojom",
+  ]
+}