exo: Add support for subcompositor interface.

components/exo/display.h

 // Copyright 2015 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_DISPLAY_H_
 #define COMPONENTS_EXO_DISPLAY_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory_handle.h"
 
 namespace exo {
 class SharedMemory;
 class ShellSurface;
+class SubSurface;
 class Surface;
 
 // The core display class. This class provides functions for creating surfaces
 // and is in charge of combining the contents of multiple surfaces into one
 // displayable output.
 class Display {
  public:
   Display();
   ~Display();
 
   // Creates a new surface.
   scoped_ptr<Surface> CreateSurface();
 
   // Creates a shared memory segment from |handle| of |size| with the
   // given |id|. This function takes ownership of |handle|.
   scoped_ptr<SharedMemory> CreateSharedMemory(
       const base::SharedMemoryHandle& handle,
       size_t size);
 
   // Creates a shell surface for an existing surface.
   scoped_ptr<ShellSurface> CreateShellSurface(Surface* surface);
 
+  // Creates a sub-surface for an existing surface. The sub-surface will be
+  // a child of |parent|.
+  scoped_ptr<SubSurface> CreateSubSurface(Surface* surface, Surface* parent);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Display);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_DISPLAY_H_