Limit max spatial layer to be configured through field trial (3->2) to match current limit in VP9En…

webrtc/media/engine/webrtcvideoengine2.cc

 /*
  *  Copyright (c) 2014 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 307 matching lines @@
 bool GetVp9LayersFromFieldTrialGroup(int* num_spatial_layers,
                                      int* num_temporal_layers) {
   std::string group = webrtc::field_trial::FindFullName("WebRTC-SupportVP9SVC");
   if (group.empty())
     return false;
 
   if (sscanf(group.c_str(), "EnabledByFlag_%dSL%dTL", num_spatial_layers,
              num_temporal_layers) != 2) {
     return false;
   }
-  const int kMaxSpatialLayers = 3;
+  const int kMaxSpatialLayers = 2;
   if (*num_spatial_layers > kMaxSpatialLayers || *num_spatial_layers < 1)
     return false;
 
   const int kMaxTemporalLayers = 3;
   if (*num_temporal_layers > kMaxTemporalLayers || *num_temporal_layers < 1)
     return false;
 
   return true;
 }
 
@@ skipping 2254 matching lines @@
         rtx_mapping[video_codecs[i].codec.id] !=
             fec_settings.red_payload_type) {
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket