Makes WorkspaceLayoutManager use ash/wm/common types

ash/wm/common/wm_screen_util.cc

Index: ash/wm/common/wm_screen_util.cc
diff --git a/ash/wm/common/wm_screen_util.cc b/ash/wm/common/wm_screen_util.cc
index dc96aa75fc0361d592782ca3b2826994d1e00f02..961fbf51e378cb0ec104416d3e449f8c7c6dad4a 100644
--- a/ash/wm/common/wm_screen_util.cc
+++ b/ash/wm/common/wm_screen_util.cc
@@ -12,8 +12,12 @@ namespace ash {
 namespace wm {
 
 gfx::Rect GetDisplayWorkAreaBoundsInParent(WmWindow* window) {
+  return GetDisplayWorkAreaBounds(window->GetParent());
+}
+
+gfx::Rect GetDisplayWorkAreaBounds(WmWindow* window) {
   gfx::Display display = window->GetDisplayNearestWindow();
-  return window->GetParent()->ConvertRectFromScreen(display.work_area());
+  return window->ConvertRectFromScreen(display.work_area());
 }
 
 gfx::Rect GetDisplayBoundsInParent(WmWindow* window) {