Add DesktopCapturerId and attach it to DesktopFrame

webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 76 matching lines @@
   // Emit the current frame.
   std::unique_ptr<DesktopFrame> frame = queue_.current_frame()->Share();
   frame->set_dpi(DesktopVector(
       GetDeviceCaps(desktop_dc_, LOGPIXELSX),
       GetDeviceCaps(desktop_dc_, LOGPIXELSY)));
   frame->mutable_updated_region()->SetRect(
       DesktopRect::MakeSize(frame->size()));
   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));
 }
 
 bool ScreenCapturerWinGdi::GetSourceList(SourceList* sources) {
   return webrtc::GetScreenList(sources);
 }
 
 bool ScreenCapturerWinGdi::SelectSource(SourceId id) {
   bool valid = IsScreenValid(id, &current_device_key_);
   if (valid)
@@ skipping 115 matching lines @@
   }
 
   // Select back the previously selected object to that the device contect
   // could be destroyed independently of the bitmap if needed.
   SelectObject(memory_dc_, previous_object);
 
   return result;
 }
 
 }  // namespace webrtc