Demonstrate external-window-mode in mus-demo

services/ui/display/platform_screen.h

Index: services/ui/display/platform_screen.h
diff --git a/services/ui/display/platform_screen.h b/services/ui/display/platform_screen.h
index c266a57ee95adfc706c3baadb29653225479ad9a..f76d25975a9bc0aa4763332640e5654b71a1cdcd 100644
--- a/services/ui/display/platform_screen.h
+++ b/services/ui/display/platform_screen.h
@@ -20,6 +20,11 @@ namespace display {
 // attached physical displays.
 class PlatformScreen {
  public:
+  enum WindowMode {
+    WINDOW_MODE_EXTERNAL,
+    WINDOW_MODE_INTERNAL,
+  };
+
   PlatformScreen();
   virtual ~PlatformScreen();
 
@@ -30,12 +35,14 @@ class PlatformScreen {
   // Registers Mojo interfaces provided.
   virtual void AddInterfaces(service_manager::InterfaceRegistry* registry) = 0;
 
-  // Triggers initial display configuration to start. On device this will
-  // configuration the connected displays. Off device this will create one or
-  // more fake displays and pretend to configure them. A non-null |delegate|
-  // must be provided that will receive notifications when displays are added,
-  // removed or modified.
-  virtual void Init(PlatformScreenDelegate* delegate) = 0;
+  // If |window_mode| == WINDOW_MODE_EXTERNAL, no initial displays are created
+  // or initialized.  Otherwise, triggers initial display configuration to
+  // start. On device this will configure the connected displays. Off device
+  // this will create one or more fake displays and pretend to configure them. A
+  // non-null |delegate| must be provided that will receive notifications when
+  // displays are added, removed or modified.
+  virtual void Init(PlatformScreenDelegate* delegate,
+                    WindowMode window_mode) = 0;
 
   // Handle requests from the platform to close a display.
   virtual void RequestCloseDisplay(int64_t display_id) = 0;