mash: Partially migrate WorkspaceController to ash common.

ash/aura/wm_root_window_controller_aura.cc

Index: ash/aura/wm_root_window_controller_aura.cc
diff --git a/ash/aura/wm_root_window_controller_aura.cc b/ash/aura/wm_root_window_controller_aura.cc
index 58a6459035126fa9b7bbc713d690d2fc49fac975..aa27ee8ab6398c4bbb4b6848d514ab3387ff0747 100644
--- a/ash/aura/wm_root_window_controller_aura.cc
+++ b/ash/aura/wm_root_window_controller_aura.cc
@@ -76,6 +76,8 @@ WmShell* WmRootWindowControllerAura::GetShell() {
 }
 
 wm::WorkspaceWindowState WmRootWindowControllerAura::GetWorkspaceWindowState() {
+  if (!root_window_controller_->workspace_controller())
+    return wm::WORKSPACE_WINDOW_STATE_DEFAULT;
   return root_window_controller_->workspace_controller()->GetWindowState();
 }