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

mash/wm/window_manager_application.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 "mash/wm/window_manager_application.h"
 
 #include "components/mus/common/util.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_tree_connection.h"
 #include "components/mus/public/cpp/window_tree_host_factory.h"
@@ skipping 39 matching lines @@
 }
 
 void WindowManagerApplication::OnEmbed(mus::Window* root) {
   root_ = root;
   root_->AddObserver(this);
   CreateContainers();
   background_layout_.reset(new BackgroundLayout(
       GetWindowForContainer(mash::wm::mojom::CONTAINER_USER_BACKGROUND)));
   shelf_layout_.reset(new ShelfLayout(
       GetWindowForContainer(mash::wm::mojom::CONTAINER_USER_SHELF)));
+
+  mus::Window* window =
+      GetWindowForContainer(mash::wm::mojom::CONTAINER_USER_WINDOWS);
   window_layout_.reset(new WindowLayout(
       GetWindowForContainer(mash::wm::mojom::CONTAINER_USER_WINDOWS)));
+  host_->AddActivationParent(window->id());
 
   window_manager_.reset(new WindowManagerImpl(this));
 
   ui_init_.reset(new ui::mojo::UIInit(views::GetDisplaysFromWindow(root)));
   aura_init_.reset(new views::AuraInit(app_, "mash_wm_resources.pak"));
 
   for (auto request : requests_)
     window_manager_binding_.AddBinding(window_manager_.get(), request->Pass());
   requests_.clear();
 }
@@ skipping 47 matching lines @@
        container < static_cast<uint16_t>(mash::wm::mojom::CONTAINER_COUNT);
        ++container) {
     mus::Window* window = root_->connection()->NewWindow();
     DCHECK_EQ(mus::LoWord(window->id()), container)
         << "Containers must be created before other windows!";
     window->SetBounds(root_->bounds());
     window->SetVisible(true);
     root_->AddChild(window);
   }
 }