Adds DesktopWindowTreeHostMus

ui/views/test/scoped_views_test_helper.cc

 // 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.
 
 #include "ui/views/test/scoped_views_test_helper.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 24 matching lines @@
     old_context_factory = aura::Env::GetInstance()->context_factory();
     DCHECK(old_context_factory);
   }
 #endif
   ui::ContextFactory* context_factory =
       ui::InitializeContextFactoryForTests(enable_pixel_output);
   views_delegate_->set_context_factory(context_factory);
 
   test_helper_.reset(ViewsTestHelper::Create(base::MessageLoopForUI::current(),
                                              context_factory));
+  platform_test_helper_->OnTestHelperCreated(test_helper_.get());
   test_helper_->SetUp();
 
 #if defined(USE_AURA)
   // When running inside mus, the context-factory from
   // ui::InitializeContextFactoryForTests() is only needed for the default
   // WindowTreeHost instance created by TestScreen. After that, the
   // context-factory is used when creating Widgets (to set-up the compositor for
   // the corresponding ui::Windows). So restore the context-factory (which
   // WindowManagerConnection would have set up), so that NativeWidgetMus
   // installs the correct context-factory that can talk to mus.
@@ skipping 16 matching lines @@
   platform_test_helper_.reset();
 
   ui::TerminateContextFactoryForTests();
 }
 
 gfx::NativeWindow ScopedViewsTestHelper::GetContext() {
   return test_helper_->GetContext();
 }
 
 }  // namespace views