Export symbols needed by the Chromium component build (part 8).

This CL uses RTC_EXPORT (defined in rtc_base/system/rtc_export.h)
to mark WebRTC symbols as visible from a shared library, this doesn't
mean these symbols are part of the public API (please continue to refer
to [1] for info about what is considered public WebRTC API).

[1] - https://webrtc.googlesource.com/src/+/HEAD/native-api.md

Bug: webrtc:9419
Change-Id: Ib2c29054b2ae008f5291bd3b762a504b18534326
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/130513
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27410}
diff --git a/api/rtp_parameters.h b/api/rtp_parameters.h
index b7d7702..7fd4952 100644
--- a/api/rtp_parameters.h
+++ b/api/rtp_parameters.h
@@ -87,7 +87,7 @@
   BALANCED,
 };
 
-extern const double kDefaultBitratePriority;
+RTC_EXPORT extern const double kDefaultBitratePriority;
 
 struct RtcpFeedback {
   RtcpFeedbackType type = RtcpFeedbackType::CCM;
@@ -362,7 +362,7 @@
   bool operator!=(const RtpRtxParameters& o) const { return !(*this == o); }
 };
 
-struct RtpEncodingParameters {
+struct RTC_EXPORT RtpEncodingParameters {
   RtpEncodingParameters();
   RtpEncodingParameters(const RtpEncodingParameters&);
   ~RtpEncodingParameters();
@@ -561,7 +561,7 @@
 // RtpCapabilities is used to represent the static capabilities of an
 // endpoint. An application can use these capabilities to construct an
 // RtpParameters.
-struct RtpCapabilities {
+struct RTC_EXPORT RtpCapabilities {
   RtpCapabilities();
   ~RtpCapabilities();