Add PlatformScreenDelegate and start implementation.

services/ui/display/platform_screen_delegate.h

+// Copyright 2016 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_DISPLAY_PLATFORM_SCREEN_DELEGATE_H_
+#define SERVICES_UI_DISPLAY_PLATFORM_SCREEN_DELEGATE_H_
+
+#include <stdint.h>
+
+namespace gfx {
+class Rect;
+}
+
+namespace display {
+
+class PlatformScreen;
+
+// The PlatformScreenDelegate will be informed of changes to the physical
+// and/or virtual displays by PlatformScreen.
+class PlatformScreenDelegate {
+ public:
+  // TODO(kylechar): We need to provide more than just the window bounds when
+  // displays are added or modified.
+
+  // Called when a display is added.
+  virtual void OnDisplayAdded(PlatformScreen* platform_screen,
+                              int64_t id,
+                              const gfx::Rect& bounds) = 0;

[sky, 2016/08/25 23:40:31]

Please clarify what the units are here. DIP or pixel.

[kylechar, 2016/08/26 13:21:19]

Done.

+
+  // Called when a display is removed.
+  virtual void OnDisplayRemoved(int64_t id) = 0;
+
+  // Called when a display is modified.
+  virtual void OnDisplayModified(int64_t id, const gfx::Rect& bounds) = 0;
+
+ protected:
+  virtual ~PlatformScreenDelegate() {}
+};
+
+}  // namespace display
+
+#endif  // SERVICES_UI_DISPLAY_PLATFORM_SCREEN_DELEGATE_H_