mash: Move directly linked NewWindowDelegate to mojom::NewWindowClient.

ash/mus/shell_delegate_mus.cc

Index: ash/mus/shell_delegate_mus.cc
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index bb6bf7561dd581c71bcbac2dc5675d6c1255695b..adc055cffb7400fe2f01ae2225a9520018cce69b 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -13,7 +13,6 @@
 #include "ash/common/wm_shell.h"
 #include "ash/mus/accessibility_delegate_mus.h"
 #include "ash/mus/context_menu_mus.h"
-#include "ash/mus/new_window_delegate_mus.h"
 #include "ash/mus/shelf_delegate_mus.h"
 #include "ash/mus/wallpaper_delegate_mus.h"
 #include "base/memory/ptr_util.h"
@@ -199,10 +198,6 @@ AccessibilityDelegate* ShellDelegateMus::CreateAccessibilityDelegate() {
   return new AccessibilityDelegateMus(connector_);
 }
 
-NewWindowDelegate* ShellDelegateMus::CreateNewWindowDelegate() {
-  return new mus::NewWindowDelegateMus;
-}
-
 MediaDelegate* ShellDelegateMus::CreateMediaDelegate() {
   // TODO: http://crbug.com/647409.
   NOTIMPLEMENTED() << " Using a stub MediaDelegate implementation";