Remove DCHECK in WmWindowMus::CloseWidget()

And improve comment. Additionally removes some dead includes in
RootWindowController.

BUG=671246
TEST=none
R=jamescook@chromium.org

Review-Url: https://codereview.chromium.org/2610853012
Cr-Commit-Position: refs/heads/master@{#442029}

ash/mus/bridge/wm_window_mus.cc

@@ -75,15 +75,15 @@ WmShell* WmWindowMus::GetShell() const {
 }
 
 void WmWindowMus::CloseWidget() {
-  views::Widget* widget = views::Widget::GetWidgetForNativeView(aura_window());
-  DCHECK(widget);
-  // Allow the client to service the close request for remote widgets.
+  // NOTE: in the FOR_CLIENT case there is not necessarily a widget associated
+  // with the window. Mash only creates widgets for top level windows if mash
+  // renders the non-client frame.
   if (aura_window()->GetProperty(kWidgetCreationTypeKey) ==
       WidgetCreationType::FOR_CLIENT) {
     WmShellMus::Get()->window_manager()->window_manager_client()->RequestClose(
         aura_window());
   } else {
-    widget->Close();
+    WmWindowAura::CloseWidget();
   }
 }
 

ash/root_window_controller.cc

@@ -66,9 +66,6 @@
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_observer.h"
 #include "ui/aura/window_tracker.h"
-#include "ui/display/display.h"
-#include "ui/display/manager/display_manager.h"
-#include "ui/display/screen.h"
 #include "ui/display/types/display_constants.h"
 #include "ui/keyboard/keyboard_controller.h"
 #include "ui/keyboard/keyboard_util.h"