cros: Fix missing gaia in single process mash

In single process mash, gaia dialog widget goes through the
following stack:
  WindowServiceDelegateImpl::SetModalType ->
  wm::GetDefaultParent ->
  GetSystemModalContainer

It does not have a |transient_parent| and hence assumed to be
a user window and put into SystemModalContainer instead of
LockSystemModalContainer.

Since the dialog widget is created with a proper container parent,
the CL fixes the issue by re-using existing container parent in
GetSystemModalContainer.

Bug: 876329
Change-Id: Iaf38273e852738b7d258a82f76dae9952051a08d
Reviewed-on: https://chromium-review.googlesource.com/1185406
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585278}

ash/public/cpp/shell_window_ids.h

@@ -184,6 +184,12 @@ const int32_t kAllShellContainerIds[] = {
     kShellWindowId_PowerButtonAnimationContainer,
 };
 
+// A list of system modal container IDs. The order of the list is important that
+// the more restrictive container appears before the less restrictive ones.
+const int32_t kSystemModalContainerIds[] = {
+    kShellWindowId_LockSystemModalContainer,
+    kShellWindowId_SystemModalContainer};
+
 // These are the list of container ids of containers which may contain windows
 // that need to be activated.
 ASH_PUBLIC_EXPORT extern const int32_t kActivatableShellWindowIds[];

ash/shell.cc

@@ -365,12 +365,8 @@ int Shell::GetOpenSystemModalWindowContainerId() {
 
   // Traverse all system modal containers, and find its direct child window
   // with "SystemModal" setting, and visible.
-  // Note: LockSystemModalContainer is more restrictive, so make it preferable
-  // to SystemModalCotainer.
-  constexpr int modal_window_ids[] = {kShellWindowId_LockSystemModalContainer,
-                                      kShellWindowId_SystemModalContainer};
   for (aura::Window* root : Shell::GetAllRootWindows()) {
-    for (int modal_window_id : modal_window_ids) {
+    for (int modal_window_id : kSystemModalContainerIds) {
       aura::Window* system_modal = root->GetChildById(modal_window_id);
       if (!system_modal)
         continue;

ash/wm/container_finder.cc

@@ -35,10 +35,18 @@ bool HasTransientParentWindow(const aura::Window* window) {
 
 aura::Window* GetSystemModalContainer(aura::Window* root,
                                       aura::Window* window) {
-  aura::Window* transient_parent = ::wm::GetTransientParent(window);
   DCHECK_EQ(ui::MODAL_TYPE_SYSTEM,
             window->GetProperty(aura::client::kModalKey));
 
+  // If |window| is already in a system modal container in |root|, re-use it.
+  for (auto modal_container_id : kSystemModalContainerIds) {
+    aura::Window* modal_container = root->GetChildById(modal_container_id);
+    if (window->parent() == modal_container)
+      return modal_container;
+  }
+
+  aura::Window* transient_parent = ::wm::GetTransientParent(window);
+
   // If screen lock is not active and user session is active,
   // all modal windows are placed into the normal modal container.
   // In case of missing transient parent (it could happen for alerts from

ash/ws/window_service_delegate_impl.cc

@@ -195,8 +195,12 @@ void WindowServiceDelegateImpl::SetModalType(aura::Window* window,
   window->SetProperty(aura::client::kModalKey, type);
 
   // Reparent the window if it will become, or will no longer be, system modal.
-  if (type == ui::MODAL_TYPE_SYSTEM || old_type == ui::MODAL_TYPE_SYSTEM)
-    wm::GetDefaultParent(window, window->GetBoundsInScreen())->AddChild(window);
+  if (type == ui::MODAL_TYPE_SYSTEM || old_type == ui::MODAL_TYPE_SYSTEM) {
+    aura::Window* const parent =
+        wm::GetDefaultParent(window, window->GetBoundsInScreen());
+    if (parent != window->parent())
+      parent->AddChild(window);
+  }
 }
 
 ui::SystemInputInjector* WindowServiceDelegateImpl::GetSystemInputInjector() {