message: Mark Cricket::VideoEncoder as RTC_EXPORT
  Without this, VideoAdapter can't be invoked from Chrome in WebrtcVideoTrackSource
  Cr-Commit-Position: refs/heads/master@{#32050}
diff: #include "media/base/video_common.h"
  #include "rtc_base/constructor_magic.h"
  #include "rtc_base/synchronization/mutex.h"
  +#include "rtc_base/system/rtc_export.h"
  #include "rtc_base/thread_annotations.h"
  namespace cricket {
  @@ -28,7 +29,7 @@ namespace cricket {
  // specified input and output formats. The adaptation includes dropping frames
  // to reduce frame rate and scaling frames.
  // VideoAdapter is thread safe.
  -class VideoAdapter {
  +class RTC_EXPORT VideoAdapter {
  public:
  VideoAdapter();
  // The source requests output frames whose width and height are divisible
  