Add metro driver and delegate_execute to GN build.

win8/metro_driver/ime/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.
+
+source_set("ime") {
+  visibility = [ "//win8/metro_driver/*" ]
+  sources = [
+    "ime_popup_monitor.cc",
+    "ime_popup_monitor.h",
+    "ime_popup_observer.h",
+    "input_scope.cc",
+    "input_scope.h",
+    "input_source.cc",
+    "input_source.h",
+    "input_source_observer.h",
+    "text_service.cc",
+    "text_service.h",
+    "text_service_delegate.h",
+    "text_store.cc",
+    "text_store.h",
+    "text_store_delegate.h",
+  ]
+
+  deps = [
+    "//base",
+    "//ui/base",
+    "//ui/metro_viewer",
+  ]
+}