Allow GCC 4.9 to compile Chromium

webrtc/modules/desktop_capture/screen_capturer_x11.cc

Index: webrtc/modules/desktop_capture/screen_capturer_x11.cc
diff --git a/webrtc/modules/desktop_capture/screen_capturer_x11.cc b/webrtc/modules/desktop_capture/screen_capturer_x11.cc
index a6f4f91838ea7bacef11024fafeec373ade03e82..b4f3bf575b84e64acb4f3d231c0d024bff50c365 100644
--- a/webrtc/modules/desktop_capture/screen_capturer_x11.cc
+++ b/webrtc/modules/desktop_capture/screen_capturer_x11.cc
@@ -412,7 +412,7 @@ std::unique_ptr<DesktopCapturer> DesktopCapturer::CreateRawScreenCapturer(
     return nullptr;
   }
 
-  return capturer;
+  return std::move(capturer);
 }
 
 }  // namespace webrtc