Break out parsing of FMTP lines so that others can use it

Intended use is to convert between different representations of "codec".

Bug: webrtc:42226302
Change-Id: If6d985ad17c2ff6018c77c7858e602b9eefa9297
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/350562
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42319}
diff --git a/pc/webrtc_sdp.h b/pc/webrtc_sdp.h
index 052ed54..a67a9b4 100644
--- a/pc/webrtc_sdp.h
+++ b/pc/webrtc_sdp.h
@@ -112,6 +112,11 @@
 bool WriteFmtpParameters(const webrtc::CodecParameterMap& parameters,
                          rtc::StringBuilder* os);
 
+// Parses a string into an FMTP parameter set, in key-value format.
+bool ParseFmtpParameterSet(absl::string_view line_params,
+                           webrtc::CodecParameterMap& codec_params,
+                           SdpParseError* error);
+
 }  // namespace webrtc
 
 #endif  // PC_WEBRTC_SDP_H_