Add NtpTimeMs as a method in EncodedImage.

Bug: b/151082828
Change-Id: Idaa6848f952f9cc9458899680d19ddf338a3ace1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/170044
Commit-Queue: Minyue Li <minyue@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30729}

modules/video_coding/encoded_frame.h

@@ -56,6 +56,7 @@ class RTC_EXPORT VCMEncodedFrame : protected EncodedImage {
   using EncodedImage::ColorSpace;
   using EncodedImage::data;
   using EncodedImage::GetEncodedData;
+  using EncodedImage::NtpTimeMs;
   using EncodedImage::PacketInfos;
   using EncodedImage::Retain;
   using EncodedImage::set_size;