Refactors StackingController::GetDefaultParent to ash/wm/common

ash/wm/aura/wm_globals_aura.cc

Index: ash/wm/aura/wm_globals_aura.cc
diff --git a/ash/wm/aura/wm_globals_aura.cc b/ash/wm/aura/wm_globals_aura.cc
index c9c9d38eab303ca549b02f5006e02ff1991340c8..8600c83aee3524ef656486b2540a89ce09428f6d 100644
--- a/ash/wm/aura/wm_globals_aura.cc
+++ b/ash/wm/aura/wm_globals_aura.cc
@@ -74,6 +74,10 @@ bool WmGlobalsAura::IsForceMaximizeOnFirstRun() {
   return Shell::GetInstance()->delegate()->IsForceMaximizeOnFirstRun();
 }
 
+bool WmGlobalsAura::IsUserSessionBlocked() {
+  return Shell::GetInstance()->session_state_delegate()->IsUserSessionBlocked();
+}
+
 bool WmGlobalsAura::IsScreenLocked() {
   return Shell::GetInstance()->session_state_delegate()->IsScreenLocked();
 }