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/rtc_base/rtc_certificate_generator.h b/rtc_base/rtc_certificate_generator.h
index 8cabca4..7c91163 100644
--- a/rtc_base/rtc_certificate_generator.h
+++ b/rtc_base/rtc_certificate_generator.h
@@ -18,6 +18,7 @@
 #include "rtc_base/ref_count.h"
 #include "rtc_base/rtc_certificate.h"
 #include "rtc_base/ssl_identity.h"
+#include "rtc_base/system/rtc_export.h"
 #include "rtc_base/thread.h"
 
 namespace rtc {
@@ -53,7 +54,8 @@
 // The static function |GenerateCertificate| generates a certificate on the
 // current thread. The |RTCCertificateGenerator| instance generates certificates
 // asynchronously on the worker thread with |GenerateCertificateAsync|.
-class RTCCertificateGenerator : public RTCCertificateGeneratorInterface {
+class RTC_EXPORT RTCCertificateGenerator
+    : public RTCCertificateGeneratorInterface {
  public:
   // Generates a certificate on the current thread. Returns null on failure.
   // If |expires_ms| is specified, the certificate will expire in approximately