Add PlatformScreenDelegate and start implementation.

services/ui/ws/user_display_manager_delegate.h

Index: services/ui/ws/user_display_manager_delegate.h
diff --git a/services/ui/ws/display_manager_delegate.h b/services/ui/ws/user_display_manager_delegate.h
similarity index 62%
rename from services/ui/ws/display_manager_delegate.h
rename to services/ui/ws/user_display_manager_delegate.h
index b5e7ec4c5f96272f6c0228fe95af74197d4b02cd..69b727fa778dcdea7ec1c85b91d988a9f63cd903 100644
--- a/services/ui/ws/display_manager_delegate.h
+++ b/services/ui/ws/user_display_manager_delegate.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SERVICES_UI_WS_DISPLAY_MANAGER_DELEGATE_H_
-#define SERVICES_UI_WS_DISPLAY_MANAGER_DELEGATE_H_
+#ifndef SERVICES_UI_WS_USER_DISPLAY_MANAGER_DELEGATE_H_
+#define SERVICES_UI_WS_USER_DISPLAY_MANAGER_DELEGATE_H_
 
 #include "services/ui/public/interfaces/display.mojom.h"
 #include "services/ui/ws/user_id.h"
@@ -14,25 +14,19 @@ namespace ws {
 class Display;
 class WindowManagerState;
 
-class DisplayManagerDelegate {
+class UserDisplayManagerDelegate {
  public:
-  virtual void OnFirstDisplayReady() = 0;
-  virtual void OnNoMoreDisplays() = 0;
-
   // Gets the frame decorations for the specified user. Returns true if the
   // decorations have been set, false otherwise. |values| may be null.
   virtual bool GetFrameDecorationsForUser(
       const UserId& user_id,
       mojom::FrameDecorationValuesPtr* values) = 0;
 
-  virtual WindowManagerState* GetWindowManagerStateForUser(
-      const UserId& user_id) = 0;
-
  protected:
-  virtual ~DisplayManagerDelegate() {}
+  virtual ~UserDisplayManagerDelegate() {}
 };
 
 }  // namespace ws
 }  // namespace ui
 
-#endif  // SERVICES_UI_WS_DISPLAY_MANAGER_DELEGATE_H_
+#endif  // SERVICES_UI_WS_USER_DISPLAY_MANAGER_DELEGATE_H_