Use webrtc::DesktopCapturer for screen capturer implementation.

media/video/capture/screen/shared_desktop_frame.h

Index: media/video/capture/screen/shared_desktop_frame.h
diff --git a/media/video/capture/screen/shared_desktop_frame.h b/media/video/capture/screen/shared_desktop_frame.h
new file mode 100644
index 0000000000000000000000000000000000000000..0ee75b16dcc4bdeae6d0a2d9023c2ce26b7ab6fa
--- /dev/null
+++ b/media/video/capture/screen/shared_desktop_frame.h
@@ -0,0 +1,43 @@
+// Copyright 2013 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 MEDIA_VIDEO_CAPTURE_SCREEN_SHARED_DESKTOP_FRAME_H_
+#define MEDIA_VIDEO_CAPTURE_SCREEN_SHARED_DESKTOP_FRAME_H_
+
+#include "base/memory/ref_counted.h"
+#include "third_party/webrtc/modules/desktop_capture/desktop_frame.h"
+
+namespace media {
+
+// SharedDesktopFrame is a DesktopFrame that may have multiple instances all
+// sharing the same buffer.
+class SharedDesktopFrame : public webrtc::DesktopFrame {
+ public:
+  virtual ~SharedDesktopFrame();
+
+  static SharedDesktopFrame* Wrap(webrtc::DesktopFrame* desktop_frame);
+
+  // Returns underlying instance of DesktopFrame.

[alexeypa (please no reviews), 2013/05/13 17:02:00]

nit: Returns the underlying instance...

[Sergey Ulanov, 2013/05/13 21:16:52]

Done.

+  webrtc::DesktopFrame* GetUnderlyingFrame();
+
+  // Creates a clone of this object.
+  SharedDesktopFrame* Share();

[alexeypa (please no reviews), 2013/05/13 17:02:00]

nit: Share() -> Clone()?

[Sergey Ulanov, 2013/05/13 21:16:52]

I think it's better to call it Share() because the class is called
SharedDesktopFrame and there is IsNotShared().

+
+  // Checks if the frame is currently shared or not. If it returns true it's
+  // guaranteed that there are no clones of the object.
+  bool IsNotShared();

[alexeypa (please no reviews), 2013/05/13 17:02:00]

nit: IsShared() is shorter and can always be negated if needed.

[Sergey Ulanov, 2013/05/13 21:16:52]

Done.

+
+ private:
+  class Core;
+
+  SharedDesktopFrame(scoped_refptr<Core> core);
+
+  scoped_refptr<Core> core_;

[alexeypa (please no reviews), 2013/05/13 17:02:00]

nit: You don't really need a full blown Core class. How about this:

typedef scoped_ptr<webrtc::DesktopFrame> Frame;
scoped_refptr<Frame> frame_; 

[Sergey Ulanov, 2013/05/13 21:16:52]

I'm not sure how that would work - scoped_ptr<> doesn't have AddRef() and
RemoveRef() methods, so scoped_refptr<Frame> will fail to compile.

[alexeypa (please no reviews), 2013/05/13 22:37:37]

Yes, you are right. That totally wouldn't work. :(

+
+  DISALLOW_COPY_AND_ASSIGN(SharedDesktopFrame);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_VIDEO_CAPTURE_SCREEN_SHARED_DESKTOP_FRAME_H_