Introduce mash/shell

mash/wm/shelf_layout.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/shelf_layout.h"
 
 #include "components/mus/public/cpp/property_type_converters.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_property.h"
 #include "mash/wm/property_util.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace mash {
 namespace wm {
 
 ShelfLayout::ShelfLayout(mus::Window* owner) : LayoutManager(owner) {
   AddLayoutProperty(mus::mojom::WindowManager::kPreferredSize_Property);
 }
 ShelfLayout::~ShelfLayout() {}
 
-void ShelfLayout::WindowAdded(mus::Window* window) {
-  DCHECK_EQ(owner()->children().size(), 1U);
-}
+// We explicitly don't make assertions about the number of children in this
+// layout as the number of children can vary when the application providing the
+// shelf restarts.
 
 void ShelfLayout::LayoutWindow(mus::Window* window) {
   gfx::Size preferred_size = GetWindowPreferredSize(window);
 
   gfx::Rect container_bounds = owner()->bounds();
   container_bounds.set_origin(
       gfx::Point(0, container_bounds.height() - preferred_size.height()));
   window->SetBounds(container_bounds);
 }
 
 }  // namespace wm
 }  // namespace mash