Support creation of toplevel mus::Windows on separate displays

ash/mus/root_window_controller.cc

Index: ash/mus/root_window_controller.cc
diff --git a/ash/mus/root_window_controller.cc b/ash/mus/root_window_controller.cc
index f5da782f9ba624961ad47415a11f907d94d743bb..d81f7f4ec5c5dc600d9307c79c3689888ba67ec3 100644
--- a/ash/mus/root_window_controller.cc
+++ b/ash/mus/root_window_controller.cc
@@ -102,9 +102,11 @@ ui::Window* RootWindowController::NewTopLevelWindow(
   if (GetRequestedContainer(window, &container_id)) {
     container_window = GetWindowByShellWindowId(container_id)->mus_window();
   } else {
-    // TODO(sky): window->bounds() isn't quite right.
+    gfx::Point origin = wm_root_window_controller_->ConvertPointToScreen(
+        WmWindowMus::Get(root_), gfx::Point());
+    gfx::Rect bounds_in_screen(origin, window->bounds().size());

[mfomitchev, 2016/11/23 23:02:12]

What if one of the window's parents is transformed? In that case
window->bounds().size() will not be equal to the visible size of the window on
the screen, no?

     container_window = WmWindowMus::GetMusWindow(wm::GetDefaultParent(
-        WmWindowMus::Get(root_), WmWindowMus::Get(window), window->bounds()));
+        WmWindowMus::Get(root_), WmWindowMus::Get(window), bounds_in_screen));
   }
   DCHECK(WmWindowMus::Get(container_window)->IsContainer());