Revert "Revert of Parse FlexFEC RTP headers in Call and add integration with BWE. (patchset #17 id:460001 of https://codereview.webrtc.org/2553863003/ )"

Problem fixed: RTP header extensions were not properly set in tests.

BUG=webrtc:5654

Review-Url: https://codereview.webrtc.org/2593963003
Cr-Commit-Position: refs/heads/master@{#15741}

webrtc/modules/rtp_rtcp/source/rtp_packet.h

@@ -31,6 +31,7 @@ class Packet {
 
   // Parse and copy given buffer into Packet.
   bool Parse(const uint8_t* buffer, size_t size);
+  bool Parse(rtc::ArrayView<const uint8_t> packet);
 
   // Parse and move given buffer into Packet.
   bool Parse(rtc::CopyOnWriteBuffer packet);