Introduce DisplayCompositor Mojo API for Mus

components/mus/surfaces/compositor_frame_sink_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 COMPONENTS_MUS_SURFACES_COMPOSITOR_FRAME_SINK_DELEGATE_H_
+#define COMPONENTS_MUS_SURFACES_COMPOSITOR_FRAME_SINK_DELEGATE_H_
+
+namespace mus {
+
+class CompositorFrameSinkImpl;
+
+// A CompositorFrameSinkDelegate decouples CompositorFrameSinks from their
+// factories enabling them to be unit tested.
+class CompositorFrameSinkDelegate {
+ public:
+  virtual void CompositorFrameSinkConnectionLost(int sink_id) = 0;
+
+  virtual cc::SurfaceId GenerateSurfaceId() = 0;
+};
+
+}  // namespace mus
+
+#endif  // COMPONENTS_MUS_SURFACES_COMPOSITOR_FRAME_SINK_DELEGATE_H_