Reland of BWE allocation strategy

TBR=stefan@webrtc.org,alexnarest@webrtc.org

Bug: webrtc:8243
Change-Id: Ie68e4f414b2ac32ba4e64877cb250fabcb089a07
Reviewed-on: https://webrtc-review.googlesource.com/13940
Commit-Queue: Alex Narest <alexnarest@webrtc.org>
Reviewed-by: Alex Narest <alexnarest@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20369}

api/peerconnectioninterface.h

@@ -786,6 +786,14 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
   // to the provided value.
   virtual RTCError SetBitrate(const BitrateParameters& bitrate) = 0;
 
+  // Sets current strategy. If not set default WebRTC allocator will be used.
+  // May be changed during an active session. The strategy
+  // ownership is passed with std::unique_ptr
+  // TODO(alexnarest): Make this pure virtual when tests will be updated
+  virtual void SetBitrateAllocationStrategy(
+      std::unique_ptr<rtc::BitrateAllocationStrategy>
+          bitrate_allocation_strategy) {}
+
   // Returns the current SignalingState.
   virtual SignalingState signaling_state() = 0;
   virtual IceConnectionState ice_connection_state() = 0;