Add coordinator for search widget in showcase.

ios/showcase/widget/sc_search_widget_coordinator.mm

+// Copyright 2017 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.
+
+#import "ios/showcase/widget/sc_search_widget_coordinator.h"
+
+#import "ios/chrome/search_widget_extension/search_widget_view_controller.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation SCSearchWidgetCoordinator
+
+@synthesize baseViewController;
+
+- (void)start {
+  SearchWidgetViewController* searchWidget =
+      [[SearchWidgetViewController alloc] init];
+  searchWidget.title = @"Search Widget";
+  searchWidget.view.backgroundColor = [UIColor whiteColor];
+  [self.baseViewController pushViewController:searchWidget animated:YES];
+}
+
+@end