Fills athena background always.

athena/system/background_controller.cc

Index: athena/system/background_controller.cc
diff --git a/athena/system/background_controller.cc b/athena/system/background_controller.cc
index acfb2802a6eae1b3e4b462259a0944e6e90b673d..5d73a6c0327a7ccca9a0517ce2af995e7b93d8ec 100644
--- a/athena/system/background_controller.cc
+++ b/athena/system/background_controller.cc
@@ -5,6 +5,7 @@
 #include "athena/system/background_controller.h"
 
 #include "athena/system/public/system_ui.h"
+#include "athena/util/fill_layout_manager.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/gfx/canvas.h"
@@ -58,9 +59,14 @@ BackgroundController::BackgroundController(aura::Window* background_container) {
   views::Widget* background_widget = new views::Widget;
   views::Widget::InitParams params(
       views::Widget::InitParams::TYPE_WINDOW_FRAMELESS);
-  params.parent = background_container;
   background_widget->Init(params);
+  background_widget->GetNativeWindow()->SetProperty(kAlwaysFillWindowKey, true);
   background_widget->GetNativeWindow()->layer()->SetMasksToBounds(true);
+  // background_widget should be reparented to |background_container| after
+  // settings kAlwaysFillWindowKey, otherwise FillLayoutManager cannot fill it
+  // properly.
+  views::Widget::ReparentNativeView(background_widget->GetNativeWindow(),
+                                    background_container);
   background_view_ = new BackgroundView;
   background_widget->SetContentsView(background_view_);
   background_widget->GetNativeView()->SetName("BackgroundWidget");