Remove hardcoded kValueSizeBytes values from variable-length header extensions.

webrtc/modules/rtp_rtcp/include/flexfec_sender.h

Index: webrtc/modules/rtp_rtcp/include/flexfec_sender.h
diff --git a/webrtc/modules/rtp_rtcp/include/flexfec_sender.h b/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
index e69daf3ff06b8360b7d4216a689d9e230c0be6a8..9e2673ab82abf8fac4847c75149b786c2c15cfb6 100644
--- a/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
+++ b/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
@@ -59,8 +59,12 @@ class FlexfecSender {
   // Returns generated FlexFEC packets.
   std::vector<std::unique_ptr<RtpPacketToSend>> GetFecPackets();
 
-  // Returns the overhead, per packet, for FlexFEC.
-  size_t MaxPacketOverhead() const;
+  // Returns the overhead, per packet, for FlexFEC. |extension_sizes| is used
+  // to calculate the RTP header extension overhead and it should have an entry
+  // for each extension that a packet might use. If only fixed-length extensions
+  // are used, |extension_sizes| should be the same at each call.
+  size_t MaxPacketOverhead(
+      rtc::ArrayView<const RtpExtensionSize> extension_sizes) const;
 
  private:
   // Utility.