Use system timestamp as capture timestamp

media/capture/video/mac/video_capture_device_mac.mm

Index: media/capture/video/mac/video_capture_device_mac.mm
diff --git a/media/capture/video/mac/video_capture_device_mac.mm b/media/capture/video/mac/video_capture_device_mac.mm
index ec6fcaf83f9279d46beea362f6b16a9814607456..432fbfbf4343231e42d82878bbd0dc5ec5886c69 100644
--- a/media/capture/video/mac/video_capture_device_mac.mm
+++ b/media/capture/video/mac/video_capture_device_mac.mm
@@ -545,18 +545,8 @@ void VideoCaptureDeviceMac::ReceiveFrame(const uint8_t* video_frame,
     return;
   }
 
-  base::TimeTicks aligned_timestamp;
-  if (timestamp == media::kNoTimestamp()) {
-    aligned_timestamp = base::TimeTicks::Now();
-  } else {
-    if (first_timestamp_ == media::kNoTimestamp()) {
-      first_timestamp_ = timestamp;
-      first_aligned_timestamp_ = base::TimeTicks::Now();
-    }
-    aligned_timestamp = first_aligned_timestamp_ + timestamp - first_timestamp_;
-  }
   client_->OnIncomingCapturedData(video_frame, video_frame_length, frame_format,
-                                  0, aligned_timestamp);
+                                  0, base::TimeTicks::Now());
 }
 
 void VideoCaptureDeviceMac::ReceiveError(