mus/views: Create a mus OSExchangeData::Provider stub, and use it.

ui/views/mus/BUILD.gn

 # Copyright 2014 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("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//services/shell/public/cpp/service.gni")
 import("//services/shell/public/service_manifest.gni")
 import("//testing/test.gni")
 import("//tools/grit/repack.gni")
@@ skipping 10 matching lines @@
     "aura_init.h",
     "clipboard_mus.cc",
     "clipboard_mus.h",
     "display_list.cc",
     "display_list.h",
     "input_method_mus.cc",
     "input_method_mus.h",
     "mus_export.h",
     "native_widget_mus.cc",
     "native_widget_mus.h",
+    "os_exchange_data_provider_mus.cc",
+    "os_exchange_data_provider_mus.h",
     "screen_mus.cc",
     "screen_mus.h",
     "screen_mus_delegate.h",
     "surface_binding.cc",
     "surface_binding.h",
     "surface_context_factory.cc",
     "surface_context_factory.h",
     "window_manager_connection.cc",
     "window_manager_connection.h",
     "window_manager_constants_converters.cc",
@@ skipping 258 matching lines @@
   type = "exe"
   name = "views_mus_unittests"
   source = "unittests_manifest.json"
 }
 
 service_manifest("interactive_ui_tests_manifest") {
   type = "exe"
   name = "views_mus_interactive_ui_tests"
   source = "interactive_ui_tests_manifest.json"
 }