Introduce window container to be used by lock screen app windows

ash/screen_util.cc

Index: ash/screen_util.cc
diff --git a/ash/screen_util.cc b/ash/screen_util.cc
index 1b674ebd37eadb88e2c691a80f3564cc8a206949..d054568a2fcbbbf89861c690f610c3a626fe1ba1 100644
--- a/ash/screen_util.cc
+++ b/ash/screen_util.cc
@@ -8,6 +8,7 @@
 #include "ash/shelf/shelf.h"
 #include "ash/shell.h"
 #include "ash/shell_port.h"
+#include "ash/wm_window.h"
 #include "base/logging.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window_event_dispatcher.h"
@@ -44,6 +45,14 @@ gfx::Rect ScreenUtil::GetDisplayWorkAreaBoundsInParent(aura::Window* window) {
 }
 
 // static
+gfx::Rect ScreenUtil::GetDisplayWorkAreaBoundsInParentForLockScreen(
+    aura::Window* window) {
+  gfx::Rect bounds = Shelf::ForWindow(window)->GetUserWorkAreaBounds();
+  ::wm::ConvertRectFromScreen(window->parent(), &bounds);
+  return bounds;
+}
+
+// static
 gfx::Rect ScreenUtil::GetDisplayBoundsWithShelf(aura::Window* window) {
   if (ShellPort::Get()->IsInUnifiedMode()) {
     // In unified desktop mode, there is only one shelf in the first display.