Add DesktopCapturerId and attach it to DesktopFrame

webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc

Index: webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc
diff --git a/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc b/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc
index 87bc195ce40e06d0f0cfe0d71d9cf78bb523435f..591adca26fb54f51b2a6d84020c8ebc8740929b7 100644
--- a/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc
+++ b/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc
@@ -94,6 +94,7 @@ void ScreenCapturerWinGdi::CaptureFrame() {
   frame->set_capture_time_ms(
       (rtc::TimeNanos() - capture_start_time_nanos) /
       rtc::kNumNanosecsPerMillisec);
+  frame->set_capturer_id(DesktopCapturerId::kScreenCapturerWinGdi);
   callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
 }