Allow parallel creation of windows

services/ui/demo/window_tree_data.cc

 // Copyright 2017 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 "services/ui/demo/window_tree_data.h"
 
 #include "base/time/time.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ skipping 49 matching lines @@
 WindowTreeData::WindowTreeData(int square_size) : square_size_(square_size) {}
 
 WindowTreeData::~WindowTreeData() {}
 
 aura::Window* WindowTreeData::bitmap_window() {
   DCHECK(!window_tree_host_->window()->children().empty());
   return window_tree_host_->window()->children()[0];
 }
 
 void WindowTreeData::Init(
     std::unique_ptr<aura::WindowTreeHostMus> window_tree_host) {

[fwang, 2017/03/16 08:59:49]

So I think you can remove the parameter and assume DCHECK(window_tree_host_)
here.

Then WindowTreeData could have a constructor that accepts a
std::unique_ptr<aura::WindowTreeHostMus> parameter and performs what is in the
if (window_tree_host) { } below.

Finally, MusDemoInternal will be able to use the constructor to append the
WindowTreeData and then call Init on the data without passing any
std::unique_ptr<aura::WindowTreeHostMus>. And MusDemoExternal won't need to pass
a nullptr (which is a bit weird).

[msisov(use msisov igalia.com), 2017/03/16 09:21:32]

If window_tree_host->InitHost(); and window_tree_host->Show() go 
into ctor, then in case of external demo, those two would be called before
OnEmbedRootReady, which is wrong, I guess.

+  DCHECK(!IsInitialized());
   if (window_tree_host) {
     window_tree_host->InitHost();
     window_tree_host->Show();
     SetWindowTreeHost(std::move(window_tree_host));
   }
 
   // Initialize the window for the bitmap.
   window_delegate_ = new aura_extra::ImageWindowDelegate();
   aura::Window* root_window = window_tree_host_->window();
   aura::Window* bitmap_window = new aura::Window(window_delegate_);
@@ skipping 32 matching lines @@
   gfx::ImageSkiaRep image_skia_rep(bitmap, 1);
   gfx::ImageSkia image_skia(image_skia_rep);
   gfx::Image image(image_skia);
 
   window_delegate_->SetImage(image);
   bitmap_window()->SchedulePaintInRect(gfx::Rect(bounds.size()));
 }
 
 }  // namespace demo
 }  // namespace ui