exo: Implement notification surface support

components/exo/display.h

Index: components/exo/display.h
diff --git a/components/exo/display.h b/components/exo/display.h
index 2d33a2e217cf567307af91d9e87bc3d35628c4f9..73bb6d7ae96a6e84221c2d7a60167318d3d9e52f 100644
--- a/components/exo/display.h
+++ b/components/exo/display.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 
 #include <memory>
+#include <string>
 
 #include "base/macros.h"
 #include "base/memory/shared_memory_handle.h"
@@ -23,6 +24,8 @@ class Point;
 }
 
 namespace exo {
+class NotificationSurface;
+class NotificationSurfaceRegistry;
 class SharedMemory;
 class ShellSurface;
 class SubSurface;
@@ -78,7 +81,18 @@ class Display {
   std::unique_ptr<SubSurface> CreateSubSurface(Surface* surface,
                                                Surface* parent);
 
+  // Creates a notification surface for a surface and notification id.
+  std::unique_ptr<NotificationSurface> CreateNotificationSurface(
+      Surface* surface,
+      const std::string& notification_id);
+
+  NotificationSurfaceRegistry* notification_surface_registry() const {
+    return notification_surface_registry_.get();
+  }
+
  private:
+  std::unique_ptr<NotificationSurfaceRegistry> notification_surface_registry_;
+
   DISALLOW_COPY_AND_ASSIGN(Display);
 };