Mus Demo: Demonstrate external window mode

ui/aura/window_tree_host.cc

 // Copyright (c) 2013 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/aura/window_tree_host.h"
 
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/cursor_client.h"
@@ skipping 19 matching lines @@
 #include "ui/gfx/icc_profile.h"
 
 namespace aura {
 
 const char kWindowTreeHostForAcceleratedWidget[] =
     "__AURA_WINDOW_TREE_HOST_ACCELERATED_WIDGET__";
 
 float GetDeviceScaleFactorFromDisplay(Window* window) {
   display::Display display =
       display::Screen::GetScreen()->GetDisplayNearestWindow(window);
-  DCHECK(display.is_valid());
+  // TODO: MusDemo fails in external mode because no display is available.

[tonikitoo, 2017/02/14 17:19:22]

fixing this should be our goal now, so that we unblock this CL.

[fwang, 2017/02/15 13:59:52]

Acknowledged.

+  // DCHECK(display.is_valid());
   return display.device_scale_factor();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // WindowTreeHost, public:
 
 WindowTreeHost::~WindowTreeHost() {
   DCHECK(!compositor_) << "compositor must be destroyed before root window";
   if (owned_input_method_) {
     delete input_method_;
@@ skipping 296 matching lines @@
   client::CursorClient* cursor_client = client::GetCursorClient(window());
   if (cursor_client) {
     const display::Display& display =
         display::Screen::GetScreen()->GetDisplayNearestWindow(window());
     cursor_client->SetDisplay(display);
   }
   dispatcher()->OnCursorMovedToRootLocation(root_location);
 }
 
 }  // namespace aura