Add PlatformScreenDelegate and start implementation.

services/ui/ws/window_server_delegate.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_
 #define SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 29 matching lines @@
   // been set.
   virtual void CreateDefaultDisplays() = 0;
 
   // Called once when the AcceleratedWidget of a Display is available.
   virtual void OnFirstDisplayReady();
 
   virtual void OnNoMoreDisplays() = 0;
 
   virtual bool IsTestConfig() const = 0;
 
+  // Called when touchscreen coordinate transforms should be updated. For
+  // example when displays or touch input devices are added/removed.
+  virtual void UpdateTouchTransforms() = 0;
+
   // Creates a WindowTreeBinding. Default implementation returns null, which
   // creates DefaultBinding.
   virtual std::unique_ptr<WindowTreeBinding> CreateWindowTreeBinding(
       BindingType type,
       ws::WindowServer* window_server,
       ws::WindowTree* tree,
       mojom::WindowTreeRequest* tree_request,
       mojom::WindowTreeClientPtr* client);
 
  protected:
   virtual ~WindowServerDelegate() {}
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_