Enabling spatial layers in VP9Impl. Filter layers in the loopback test.

webrtc/modules/rtp_rtcp/source/rtp_format_vp9.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 560 matching lines @@
                                   bool* last_packet) {
   if (packets_.empty()) {
     return false;
   }
   PacketInfo packet_info = packets_.front();
   packets_.pop();
 
   if (!WriteHeaderAndPayload(packet_info, buffer, bytes_to_send)) {
     return false;
   }
-  *last_packet = packets_.empty();
+  *last_packet =
+      packets_.empty() && (hdr_.spatial_idx == kNoSpatialIdx ||
+                           hdr_.spatial_idx == hdr_.num_spatial_layers - 1);
   return true;
 }
 
 // VP9 format:
 //
 // Payload descriptor for F = 1 (flexible mode)
 //       0 1 2 3 4 5 6 7
 //      +-+-+-+-+-+-+-+-+
 //      |I|P|L|F|B|E|V|-| (REQUIRED)
 //      +-+-+-+-+-+-+-+-+
@@ skipping 162 matching lines @@
   if (parsed_payload->payload_length == 0) {
     LOG(LS_ERROR) << "Failed parsing VP9 payload data.";
     return false;
   }
   parsed_payload->payload =
       payload + payload_length - parsed_payload->payload_length;
 
   return true;
 }
 }  // namespace webrtc