mus: Allow the WM to specify the windows that can have active children.

components/mus/public/cpp/tests/window_server_test_base.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 "components/mus/public/cpp/tests/window_server_test_base.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/test_timeouts.h"
@@ skipping 69 matching lines @@
 
 bool WindowServerTestBase::ConfigureIncomingConnection(
     mojo::ApplicationConnection* connection) {
   connection->AddService<mojom::WindowTreeClient>(this);
   return true;
 }
 
 void WindowServerTestBase::OnEmbed(Window* root) {
   most_recent_connection_ = root->connection();
   EXPECT_TRUE(QuitRunLoop());
+  host_->AddActivationParent(root->id());
 }
 
 void WindowServerTestBase::OnConnectionLost(WindowTreeConnection* connection) {
   window_tree_connection_destroyed_ = true;
 }
 
 void WindowServerTestBase::Create(
     mojo::ApplicationConnection* connection,
     mojo::InterfaceRequest<mojom::WindowTreeClient> request) {
   WindowTreeConnection::Create(
       this, request.Pass(),
       WindowTreeConnection::CreateType::DONT_WAIT_FOR_EMBED);
 }
 
 }  // namespace mus