Add coordinator for search widget in showcase.

ios/showcase/widget/BUILD.gn

Index: ios/showcase/widget/BUILD.gn
diff --git a/ios/showcase/widget/BUILD.gn b/ios/showcase/widget/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..aca547985bee0a0f6169cbdab151214bf491e41d
--- /dev/null
+++ b/ios/showcase/widget/BUILD.gn
@@ -0,0 +1,16 @@
+# 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.
+
+source_set("widget") {
+  sources = [
+    "sc_search_widget_coordinator.h",
+    "sc_search_widget_coordinator.mm",
+  ]
+  deps = [
+    "//ios/chrome/search_widget_extension:search_widget",
+    "//ios/showcase/common",
+  ]
+  libs = [ "UIKit.framework" ]
+  configs += [ "//build/config/compiler:enable_arc" ]
+}