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

webrtc/modules/desktop_capture/cropped_desktop_frame.cc

Index: webrtc/modules/desktop_capture/cropped_desktop_frame.cc
diff --git a/webrtc/modules/desktop_capture/cropped_desktop_frame.cc b/webrtc/modules/desktop_capture/cropped_desktop_frame.cc
index 733fe9b2adf5dc244087a04411305f7dff63afb3..b26d5b0600acf27da8d7cdf4044e93605e66c589 100644
--- a/webrtc/modules/desktop_capture/cropped_desktop_frame.cc
+++ b/webrtc/modules/desktop_capture/cropped_desktop_frame.cc
@@ -19,7 +19,8 @@ namespace webrtc {
 // A DesktopFrame that is a sub-rect of another DesktopFrame.
 class CroppedDesktopFrame : public DesktopFrame {
  public:
-  CroppedDesktopFrame(DesktopFrame* frame, const DesktopRect& rect);
+  CroppedDesktopFrame(std::unique_ptr<DesktopFrame> frame,
+                      const DesktopRect& rect);
 
  private:
   std::unique_ptr<DesktopFrame> frame_;
@@ -27,23 +28,23 @@ class CroppedDesktopFrame : public DesktopFrame {
   RTC_DISALLOW_COPY_AND_ASSIGN(CroppedDesktopFrame);
 };
 
-DesktopFrame*
-CreateCroppedDesktopFrame(DesktopFrame* frame, const DesktopRect& rect) {
-  if (!DesktopRect::MakeSize(frame->size()).ContainsRect(rect)) {
-    delete frame;
-    return NULL;
-  }
+std::unique_ptr<DesktopFrame> CreateCroppedDesktopFrame(
+    std::unique_ptr<DesktopFrame> frame,
+    const DesktopRect& rect) {
+  if (!DesktopRect::MakeSize(frame->size()).ContainsRect(rect))
+    return nullptr;
 
-  return new CroppedDesktopFrame(frame, rect);
+  return std::unique_ptr<DesktopFrame>(
+      new CroppedDesktopFrame(std::move(frame), rect));
 }
 
-CroppedDesktopFrame::CroppedDesktopFrame(DesktopFrame* frame,
+CroppedDesktopFrame::CroppedDesktopFrame(std::unique_ptr<DesktopFrame> frame,
                                          const DesktopRect& rect)
     : DesktopFrame(rect.size(),
                    frame->stride(),
                    frame->GetFrameDataAtPos(rect.top_left()),
-                   frame->shared_memory()),
-      frame_(frame) {
+                   frame->shared_memory()) {
+  frame_ = std::move(frame);

[Wez, 2016/05/18 01:29:50]

Why does this need to be assignment, and not initialization?

[Sergey Ulanov, 2016/05/31 12:02:48]

initializers don't guarantee order in which arguments are evaluated, but |frame|
is used in the DesktopFrame() initialization above. Assigning it here guarantees
that |frame| is valid when evaluating arguments for the DesktopFrame()
constructor.

[Wez, 2016/06/01 21:29:04]

nit: In this case DesktopFrame() (immediate base class) should be initialized
prior to |frame_| (non-static member of this derived class) so the order is
well-defined.

Nonetheless, explicit assignment in the ctor body is fine by me.

 }
 
 }  // namespace webrtc