exo: Implement notification surface support

components/exo/notification_surface.h

Index: components/exo/notification_surface.h
diff --git a/components/exo/notification_surface.h b/components/exo/notification_surface.h
new file mode 100644
index 0000000000000000000000000000000000000000..511ab949bcbce3f16b1991f8249cc3be8aea381d
--- /dev/null
+++ b/components/exo/notification_surface.h
@@ -0,0 +1,40 @@
+// 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 COMPONENTS_EXO_NOTIFICATION_SURFACE_H_
+#define COMPONENTS_EXO_NOTIFICATION_SURFACE_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "components/exo/surface_observer.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace exo {
+class Surface;
+
+// Handles notification surface role of a given surface.
+class NotificationSurface : public SurfaceObserver {

[reveman, 2016/06/16 03:35:20]

I think this should be a SurfaceDelegate so we can handle commits properly and
we prevent the surface from being used for something else.

Also, should we be creating an aura::Window for this? Or how is this otherwise
being embedded in another part of the UI? Note that Surface is or has an
aura::Window but is wrong and will soon change.

[xiyuan, 2016/06/20 22:40:28]

Done. Made it a SurfaceDelegate and create its own aura::Window instead of using
the one from Surface. We would need to revisit this after Surface becomes a
layer though.

+ public:
+  NotificationSurface(Surface* surface, const std::string& notification_id);
+  ~NotificationSurface() override;
+
+  gfx::Size GetSize() const;
+
+  Surface* surface() { return surface_; }

[reveman, 2016/06/16 03:35:20]

Do we need to expose the Surface? What part of it is needed to draw the
notifications and handle input?

[xiyuan, 2016/06/20 22:40:29]

Right now, the surface is handled via NativeViewHost. See
arc_custom_notification_view.cc in https://codereview.chromium.org/2066853002/.

We need an aura::Window for this to work. I will refactor this class to have its
own aura::Window instead of using the one from Surface.

+  const std::string& notification_id() const { return notification_id_; }
+
+ private:
+  // SurfaceObserver

[reveman, 2016/06/16 03:35:20]

nit: "Overridden from SurfaceObserver:"

[xiyuan, 2016/06/20 22:40:28]

Done.

+  void OnSurfaceDestroying(Surface* surface) override;
+
+  Surface* surface_;  // Not owned.
+  const std::string notification_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(NotificationSurface);
+};
+
+}  // namespace exo
+
+#endif  // COMPONENTS_EXO_NOTIFICATION_SURFACE_H_