Add missing RTC_EXPORT for the component build.

Bug: webrtc:9419
Change-Id: I3225259fb4cc55e9820f590928795f4587f1e3cb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/153884
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29479}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 6fc1057..e46deea 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -226,7 +226,7 @@
 // // Close the application...
 // delete apm;
 //
-class AudioProcessing : public rtc::RefCountInterface {
+class RTC_EXPORT AudioProcessing : public rtc::RefCountInterface {
  public:
   // The struct below constitutes the new parameter scheme for the audio
   // processing. It is being introduced gradually and until it is fully