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

webrtc/modules/interface/module_common_types.h

Index: webrtc/modules/interface/module_common_types.h
diff --git a/webrtc/modules/interface/module_common_types.h b/webrtc/modules/interface/module_common_types.h
index 02ce03f15387c4ff01f57428fd0f3a263ac6e20e..61a52662868ba6de61da1a67d68b7abce209ca1a 100644
--- a/webrtc/modules/interface/module_common_types.h
+++ b/webrtc/modules/interface/module_common_types.h
@@ -160,6 +160,7 @@ struct RTPVideoHeaderVP9 {
     inter_layer_predicted = false;
     gof_idx = kNoGofIdx;
     num_ref_pics = 0;
+    num_spatial_layers = 1;
   }
 
   bool inter_pic_predicted;  // This layer frame is dependent on previously
@@ -191,7 +192,7 @@ struct RTPVideoHeaderVP9 {
   int16_t ref_picture_id[kMaxVp9RefPics];  // PictureID of reference pictures.
 
   // SS data.
-  size_t num_spatial_layers;
+  size_t num_spatial_layers;  // Always populated.
   bool spatial_layer_resolution_present;
   uint16_t width[kMaxVp9NumberOfSpatialLayers];
   uint16_t height[kMaxVp9NumberOfSpatialLayers];