Adds public API and loads Cast OSD plane implementation from shared lib

chromecast/public/osd_plane.h

Index: chromecast/public/osd_plane.h
diff --git a/chromecast/public/osd_plane.h b/chromecast/public/osd_plane.h
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index 0000000000000000000000000000000000000000..d689cba5440afa206d594137d66bc24361ee4b34
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+++ b/chromecast/public/osd_plane.h
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+// Copyright (c) 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 CHROMECAST_PUBLIC_OSD_PLANE_H_
+#define CHROMECAST_PUBLIC_OSD_PLANE_H_
+
+namespace chromecast {
+
+class OsdSurface;
+struct Rect;
+struct Size;
+
+// Abstract graphics plane for OSD, to be implemented in platform-specific way.
+// Platform must composite this plane on top of main (GL-based) graphics plane.
+class OsdPlane {
+ public:
+  virtual ~OsdPlane() {}
+
+  // Creates a surface for offscreen drawing.
+  virtual OsdSurface* CreateSurface(const Size& size) = 0;
+
+  // Sets a clip rectangle, client should call before drawing to back buffer
+  // to specify the area they intend to draw on.  Platforms may reduce memory
+  // usage by only allocating back buffer to cover this area.  Areas outside
+  // clip rectangle must display as fully transparent.  In particular, setting
+  // an empty clip rectangle and calling Flip should clear the plane.
+  virtual void SetClipRectangle(const Rect& rect) = 0;
+
+  // Gets the current back buffer surface.  Valid until next call to Flip or
+  // SetClipRectangle.
+  virtual OsdSurface* GetBackBuffer() = 0;
+
+  // Presents current back buffer to screen.
+  virtual void Flip() = 0;
+};
+
+}  // namespace chromecast
+
+#endif  // CHROMECAST_PUBLIC_OSD_PLANE_H