Converts remaining usage of WmLayoutManager to aura::LayoutManager

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index cfa0244a0941e1bb6a5d589661c51da187cfe614..bc886a1bf307d1065e5b8643c205ea6e47a598aa 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -523,7 +523,7 @@ void Shell::NotifyPinnedStateChanged(WmWindow* pinned_window) {
 }
 
 void Shell::NotifyVirtualKeyboardActivated(bool activated,
-                                           WmWindow* root_window) {
+                                           aura::Window* root_window) {
   for (auto& observer : shell_observers_)
     observer.OnVirtualKeyboardStateChanged(activated, root_window);
 }