[NOT FOR REVIEW] ash: Add some implementation for the window management extension API.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 383218d424358ebb7b14f8c58562da43951b2c78..b6cc7fbface60acadf47362b6d65621a83ff79a2 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -130,6 +130,11 @@ aura::client::UserActionClient* ShellDelegateImpl::CreateUserActionClient() {
 void ShellDelegateImpl::OpenFeedbackPage() {
 }
 
+ash::WindowManagerExtensionDelegate*
+ShellDelegateImpl::CreateWindowManagerDelegate() {
+  return NULL;
+}
+
 void ShellDelegateImpl::RecordUserMetricsAction(UserMetricsAction action) {
 }