Forward capturer_id between DesktopFrame and its implementations

webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.cc

 /*
  *  Copyright (c) 2016 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 196 matching lines @@
     }
   } else {
     frame->mutable_updated_region()->SetRect(
         DesktopRect::MakeSize(frame->size()));
   }
   last_frame_ = frame->Share();
 
   frame->set_capture_time_ms(frame->GetUnderlyingFrame()->capture_time_ms() +
                              (rtc::TimeNanos() - start_time_nanos) /
                                  rtc::kNumNanosecsPerMillisec);
+  frame->set_capturer_id(frame->GetUnderlyingFrame()->capturer_id());
   callback_->OnCaptureResult(result, std::move(frame));
 }
 
 }  // namespace webrtc