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

webrtc/modules/desktop_capture/desktop_capturer.h

Index: webrtc/modules/desktop_capture/desktop_capturer.h
diff --git a/webrtc/modules/desktop_capture/desktop_capturer.h b/webrtc/modules/desktop_capture/desktop_capturer.h
index ba70e0155373410475cff8b27a8362bae453b265..23821280999f3dfaed6f3d8ae9d400a91f3bdc76 100644
--- a/webrtc/modules/desktop_capture/desktop_capturer.h
+++ b/webrtc/modules/desktop_capture/desktop_capturer.h
@@ -15,24 +15,44 @@
 
 #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() {}