Demonstrate external-window-mode in mus-demo

services/ui/display/platform_screen_stub.cc

Index: services/ui/display/platform_screen_stub.cc
diff --git a/services/ui/display/platform_screen_stub.cc b/services/ui/display/platform_screen_stub.cc
index 8a90a4d23a3652ca0ae09d1c708afd0e4e07de66..ca2acfc4f659d7fe668d8d7710357587d89785c5 100644
--- a/services/ui/display/platform_screen_stub.cc
+++ b/services/ui/display/platform_screen_stub.cc
@@ -55,7 +55,8 @@ void PlatformScreenStub::FixedSizeScreenConfiguration() {
 void PlatformScreenStub::AddInterfaces(
     service_manager::InterfaceRegistry* registry) {}
 
-void PlatformScreenStub::Init(PlatformScreenDelegate* delegate) {
+void PlatformScreenStub::Init(PlatformScreenDelegate* delegate,
+                              WindowMode window_mode) {
   DCHECK(delegate);
   delegate_ = delegate;
   display_metrics_ = DefaultViewportMetrics();