Add system modals to the proper container in mus+ash.

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 8818e3cbdd393d96889b57860a3bdf4eaa865c69..ed4bdaad6971370bdb9d73a9035f5e688a06c092 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -38,6 +38,7 @@
 #include "services/ui/public/cpp/property_type_converters.h"
 #include "services/ui/public/interfaces/constants.mojom.h"
 #include "services/ui/public/interfaces/window_manager.mojom.h"
+#include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/window_parenting_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/mus/capture_synchronizer.h"
@@ -321,6 +322,24 @@ bool WindowManager::OnWmSetProperty(
   return false;
 }
 
+void WindowManager::OnWmSetModalType(aura::Window* window, ui::ModalType type) {

[sky, 2017/03/17 21:37:46]

I'm a little surprised we need this, but I guess that's because classic ash only
allows the modality to be set before parenting.

+  ui::ModalType old_type = window->GetProperty(aura::client::kModalKey);
+  if (type == old_type)
+    return;
+
+  window->SetProperty(aura::client::kModalKey, type);
+  if (type != ui::MODAL_TYPE_SYSTEM && old_type != ui::MODAL_TYPE_SYSTEM)
+    return;
+
+  if (window->parent())
+    window->parent()->RemoveChild(window);
+  int32_t new_container_id = type == ui::MODAL_TYPE_SYSTEM

[sky, 2017/03/17 21:37:46]

Can you use GetDefaultParent? In container_finder?

[Hadi, 2017/03/20 15:03:29]

Done.

+                                 ? kShellWindowId_SystemModalContainer
+                                 : kShellWindowId_DefaultContainer;
+  Shell::GetContainer(Shell::GetPrimaryRootWindow(), new_container_id)
+      ->AddChild(window);
+}
+
 void WindowManager::OnWmSetCanFocus(aura::Window* window, bool can_focus) {
   NonClientFrameController* non_client_frame_controller =
       NonClientFrameController::Get(window);