exo: Add support for subcompositor interface.

components/exo/sub_surface.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_SUB_SURFACE_H_
+#define COMPONENTS_EXO_SUB_SURFACE_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "components/exo/surface_delegate.h"
+#include "components/exo/surface_observer.h"
+#include "ui/gfx/geometry/point.h"
+
+namespace base {
+namespace trace_event {
+class TracedValue;
+}
+}
+
+namespace exo {
+class Surface;
+
+// This class provides functions for treating a surface as a sub-surface. A
+// sub-surface has one parent surface.
+class SubSurface : public SurfaceDelegate, public SurfaceObserver {
+ public:
+  SubSurface(Surface* surface, Surface* parent);
+  ~SubSurface() override;
+
+  // This schedules a sub-surface position change. The sub-surface will be
+  // moved so, that its origin (top-left corner pixel) will be at the |position|
+  // of the parent surface coordinate system.
+  void SetPosition(const gfx::Point& position);
+
+  // This removes sub-surface from the stack, and puts it back just above the
+  // reference surface, changing the z-order of the sub-surfaces. The reference
+  // surface must be one of the sibling surfaces, or the parent surface.
+  void PlaceAbove(Surface* reference);
+
+  // This removes sub-surface from the stack, and puts it back just below the
+  // sibling surface.
+  void PlaceBelow(Surface* sibiling);
+
+  // Change the commit behaviour of the sub-surface.
+  void SetCommitBehavior(bool synchronized);
+
+  // Returns a trace value representing the state of the surface.
+  scoped_refptr<base::trace_event::TracedValue> AsTracedValue() const;
+
+  // Overridden from SurfaceDelegate:
+  void OnSurfaceCommit() override;
+  bool IsSurfaceSynchronized() const override;
+
+  // Overridden from SurfaceObserver:
+  void OnSurfaceDestroying(Surface* surface) override;
+
+ private:
+  Surface* surface_;
+  Surface* parent_;
+  bool is_synchronized_;
+
+  DISALLOW_COPY_AND_ASSIGN(SubSurface);
+};
+
+}  // namespace exo
+
+#endif  // COMPONENTS_EXO_SUB_SURFACE_H_