Add unit test and showcase support for search widget.

ios/showcase/core/showcase_model.mm

 // Copyright 2016 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/core/showcase_model.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
@@ skipping 48 matching lines @@
     @{
       showcase::kClassForDisplayKey : @"ToolbarViewController",
       showcase::kClassForInstantiationKey : @"SCToolbarCoordinator",
       showcase::kUseCaseKey : @"Toolbar",
     },
     @{
       showcase::kClassForDisplayKey : @"UITableViewCell",
       showcase::kClassForInstantiationKey : @"UIKitTableViewCellViewController",
       showcase::kUseCaseKey : @"UIKit Table Cells",
     },
+    @{
+      showcase::kClassForDisplayKey : @"SearchWidgetViewController",
+      showcase::kClassForInstantiationKey : @"SearchWidgetViewController",
+      showcase::kUseCaseKey : @"Search Widget",
+    },
   ];
 }
 
 @end