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

webrtc/modules/desktop_capture/cropping_window_capturer.cc

Index: webrtc/modules/desktop_capture/cropping_window_capturer.cc
diff --git a/webrtc/modules/desktop_capture/cropping_window_capturer.cc b/webrtc/modules/desktop_capture/cropping_window_capturer.cc
index cbe7d96e5d637d579799cdf1581a76ef48ed5cd1..6e4a16b62e51fc1d89723b8231c889efec93dbc3 100644
--- a/webrtc/modules/desktop_capture/cropping_window_capturer.cc
+++ b/webrtc/modules/desktop_capture/cropping_window_capturer.cc
@@ -74,31 +74,29 @@ bool CroppingWindowCapturer::BringSelectedWindowToFront() {
   return window_capturer_->BringSelectedWindowToFront();
 }
 
-void CroppingWindowCapturer::OnCaptureCompleted(DesktopFrame* frame) {
-  std::unique_ptr<DesktopFrame> screen_frame(frame);
-
+void CroppingWindowCapturer::OnCaptureCompleted(
+    std::unique_ptr<DesktopFrame> screen_frame) {
   if (!ShouldUseScreenCapturer()) {
     LOG(LS_INFO) << "Window no longer on top when ScreenCapturer finishes";
     window_capturer_->Capture(DesktopRegion());
     return;
   }
 
-  if (!frame) {
+  if (!screen_frame) {
     LOG(LS_WARNING) << "ScreenCapturer failed to capture a frame";
-    callback_->OnCaptureCompleted(NULL);
+    callback_->OnCaptureCompleted(std::unique_ptr<DesktopFrame>());
     return;
   }
 
   DesktopRect window_rect = GetWindowRectInVirtualScreen();
   if (window_rect.is_empty()) {
     LOG(LS_WARNING) << "Window rect is empty";
-    callback_->OnCaptureCompleted(NULL);
+    callback_->OnCaptureCompleted(std::unique_ptr<DesktopFrame>());
     return;
   }
 
-  std::unique_ptr<DesktopFrame> window_frame(
-      CreateCroppedDesktopFrame(screen_frame.release(), window_rect));
-  callback_->OnCaptureCompleted(window_frame.release());
+  callback_->OnCaptureCompleted(
+      CreateCroppedDesktopFrame(std::move(screen_frame), window_rect));
 }
 
 #if !defined(WEBRTC_WIN)