Wires up transients for DesktopWindowTreeHostMus

ui/views/mus/desktop_window_tree_host_mus.cc

Index: ui/views/mus/desktop_window_tree_host_mus.cc
diff --git a/ui/views/mus/desktop_window_tree_host_mus.cc b/ui/views/mus/desktop_window_tree_host_mus.cc
index 478dfb93fa70c09ad16107f3db46aa0226626030..6fe0eb1422be10153da70ef11c43448e68c5f7cd 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.cc
+++ b/ui/views/mus/desktop_window_tree_host_mus.cc
@@ -46,6 +46,11 @@ void DesktopWindowTreeHostMus::Init(aura::Window* content_window,
 
 void DesktopWindowTreeHostMus::OnNativeWidgetCreated(
     const Widget::InitParams& params) {
+  if (params.parent && params.parent->GetHost()) {
+    parent_ = static_cast<DesktopWindowTreeHostMus*>(params.parent->GetHost());
+    DCHECK(parent_);

[msw, 2016/11/04 23:21:43]

nit: seems unnecessary to DCHECK a non-null value that's just been
static-casted, and is about to be dereferenced, but I'll leave it up to you.

[sky, 2016/11/04 23:30:50]

Done.

+    parent_->children_.insert(this);
+  }
   native_widget_delegate_->OnNativeWidgetCreated(true);
 }
 
@@ -72,6 +77,18 @@ void DesktopWindowTreeHostMus::Close() {
 }
 
 void DesktopWindowTreeHostMus::CloseNow() {
+  // If we have children, close them. Use a copy for iteration because they'll
+  // remove themselves from |children_|.
+  std::set<DesktopWindowTreeHostMus*> children_copy = children_;
+  for (DesktopWindowTreeHostMus* child : children_copy)

[msw, 2016/11/04 23:21:43]

totally optional nit: convert the corresponding DesktopWindowTreeHostX11 code to
better match this (member names, for-range loop, comments, etc.) or vice versa.

[sky, 2016/11/04 23:30:50]

I'm leaving that code alone.

+    child->CloseNow();
+  DCHECK(children_.empty());
+
+  if (parent_) {
+    parent_->children_.erase(this);
+    parent_ = nullptr;
+  }
+
   native_widget_delegate_->OnNativeWidgetDestroying();

[msw, 2016/11/04 23:21:43]

q: DesktopWindowTreeHostX11 orders this before child/parent destruction, is
there a reason they should differ?

[sky, 2016/11/04 23:30:50]

Good catch. Updated.

   DestroyCompositor();
   desktop_native_widget_aura_->OnHostClosed();