Use std::unique_ptr<> to pass frame ownership in DesktopCapturer impls.

webrtc/modules/desktop_capture/desktop_capturer.h

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_H_
 #define WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_H_
 
 #include <stddef.h>
 
 #include <memory>
 
+#include "webrtc/modules/desktop_capture/desktop_frame.h"
 #include "webrtc/modules/desktop_capture/desktop_capture_types.h"
 #include "webrtc/modules/desktop_capture/shared_memory.h"
 
 namespace webrtc {
 
 class DesktopFrame;
-class DesktopRegion;
 
 // Abstract interface for screen and window capturers.
 class DesktopCapturer {
  public:
+  enum class Result {
+    // The frame was captured successfully.
+    SUCCESS,
+
+    // There was a temporary error. The caller should retry capting again.

[Wez, 2016/06/01 21:29:05]

typo: capting

nit: IIUC what you mean here is that the caller should continue requesting
captures, in the expectation that it will eventually recover - suggesting
"retry" implies that the call should be retried immediately for some reason,
which I don't think is what you want?

Is this even an error condition, really? Or is it just a special form of SUCCESS
in which there is no actual pixel data?

[Sergey Ulanov, 2016/06/03 08:14:31]

Good point. Reworded the comment a bit.
I thinks it's still better to call it error, as there is no frame in the result.
It's somewhat similar to net::ERR_IO_PENDING.

+    ERROR_TEMPORARY,
+
+    // Capture has failed and will keep failing if the caller tries calling
+    // Capture() again.
+    ERROR_PERMANENT,
+  };
+
   // Interface that must be implemented by the DesktopCapturer consumers.
   class Callback {
    public:
-    // Called after a frame has been captured. Handler must take ownership of
-    // |frame|. If capture has failed for any reason |frame| is set to NULL
-    // (e.g. the window has been closed).
-    virtual void OnCaptureCompleted(DesktopFrame* frame) = 0;
+    // Called after a frame has been captured. |frame| is not nullptr iff

[Wez, 2016/06/01 21:29:05]

nit: I've been told off before for using "iff". ;)

[Sergey Ulanov, 2016/06/03 08:14:31]

Done.

+    // |result| is SUCCESS.
+    virtual void OnCaptureResult(Result result,
+                                 std::unique_ptr<DesktopFrame> frame) {
+      OnCaptureCompleted(frame.release());
+    }
+
+    // Deprecated version of the method above that uses raw pointer instead of
+    // std::unique_ptr<>.
+    // TODO(sergeyu): Remove this method and make OnCaptureResult() pure
+    // virtual. crbug.com/webrtc/5950
+    virtual void OnCaptureCompleted(DesktopFrame* frame) { delete frame; };
 
    protected:
     virtual ~Callback() {}
   };
 
   virtual ~DesktopCapturer() {}
 
   // Called at the beginning of a capturing session. |callback| must remain
   // valid until capturer is destroyed.
   virtual void Start(Callback* callback) = 0;
@@ skipping 16 matching lines @@
   // Sets the window to be excluded from the captured image in the future
   // Capture calls. Used to exclude the screenshare notification window for
   // screen capturing.
   virtual void SetExcludedWindow(WindowId window) {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_H_