views/mus: Set-up transient windows correctly.

ui/views/mus/native_widget_mus.cc

Index: ui/views/mus/native_widget_mus.cc
diff --git a/ui/views/mus/native_widget_mus.cc b/ui/views/mus/native_widget_mus.cc
index bbcc75d19d0c9b3c80ace25e087a68a838be81a9..68b98f9ae53e9dde3ab376a480e507587bc9058f 100644
--- a/ui/views/mus/native_widget_mus.cc
+++ b/ui/views/mus/native_widget_mus.cc
@@ -14,6 +14,7 @@
 #include "ui/aura/env.h"
 #include "ui/aura/layout_manager.h"
 #include "ui/aura/window.h"
+#include "ui/aura/window_property.h"
 #include "ui/base/hit_test.h"
 #include "ui/compositor/clip_transform_recorder.h"
 #include "ui/compositor/paint_recorder.h"
@@ -29,9 +30,13 @@
 #include "ui/wm/core/capture_controller.h"
 #include "ui/wm/core/focus_controller.h"
 
+DECLARE_WINDOW_PROPERTY_TYPE(mus::Window*);
+
 namespace views {
 namespace {
 
+DEFINE_WINDOW_PROPERTY_KEY(mus::Window*, kMusWindow, nullptr);
+
 WindowManagerClientAreaInsets* window_manager_client_area_insets = nullptr;
 
 // TODO: figure out what this should be.
@@ -269,6 +274,7 @@ void NativeWidgetMus::InitNativeWidget(const Widget::InitParams& params) {
       new WindowTreeHostMus(shell_, this, window_, surface_type_));
   window_tree_host_->InitHost();
   aura::Env::GetInstance()->set_context_factory(default_context_factory);
+  window_tree_host_->window()->SetProperty(kMusWindow, window_);
 
   focus_client_.reset(new wm::FocusController(new FocusRulesImpl));
 
@@ -289,8 +295,16 @@ void NativeWidgetMus::InitNativeWidget(const Widget::InitParams& params) {
   content_->Show();
   content_->SetTransparent(true);
   content_->SetFillsBoundsCompletely(false);
-
   window_tree_host_->window()->AddChild(content_);
+
+  // Set-up transiency if appropriate.
+  if (params.parent && !params.child) {
+    aura::Window* parent_root = params.parent->GetRootWindow();
+    mus::Window* parent_mus = parent_root->GetProperty(kMusWindow);
+    if (parent_mus)
+      parent_mus->AddTransientWindow(window_);
+  }
+
   // TODO(beng): much else, see [Desktop]NativeWidgetAura.
 
   native_widget_delegate_->OnNativeWidgetCreated(false);