Add frame rate parameter to SpatialLayer struct.

This will allow us to configure VP9 encoder to produce spatial layers
with different frame rates.

Bug: webrtc:9650
Change-Id: I3a9c58072003b8a8da681d5291d8f7ede7f52fa4
Reviewed-on: https://webrtc-review.googlesource.com/95427
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24435}
diff --git a/common_types.h b/common_types.h
index c1c5b4e..beb6bca 100644
--- a/common_types.h
+++ b/common_types.h
@@ -361,6 +361,7 @@
 
   unsigned short width;
   unsigned short height;
+  float maxFramerate;  // fps.
   unsigned char numberOfTemporalLayers;
   unsigned int maxBitrate;     // kilobits/sec.
   unsigned int targetBitrate;  // kilobits/sec.