Extract bitrate allocation of spatial/temporal layers out of codec impl.

webrtc/modules/video_coding/generic_encoder.cc

Index: webrtc/modules/video_coding/generic_encoder.cc
diff --git a/webrtc/modules/video_coding/generic_encoder.cc b/webrtc/modules/video_coding/generic_encoder.cc
index acef556b2425d4429b22eb73d5b77dd25f211eab..3b1c612c07c3be0494a10f5f6eb6837bcc88f100 100644
--- a/webrtc/modules/video_coding/generic_encoder.cc
+++ b/webrtc/modules/video_coding/generic_encoder.cc
@@ -28,7 +28,7 @@ VCMGenericEncoder::VCMGenericEncoder(
     : encoder_(encoder),
       vcm_encoded_frame_callback_(encoded_frame_callback),
       internal_source_(internal_source),
-      encoder_params_({0, 0, 0, 0}),
+      encoder_params_({BitrateAllocation(), 0, 0, 0}),
       is_screenshare_(false) {}
 
 VCMGenericEncoder::~VCMGenericEncoder() {}
@@ -93,8 +93,7 @@ void VCMGenericEncoder::SetEncoderParameters(const EncoderParameters& params) {
   if (channel_parameters_have_changed)
     encoder_->SetChannelParameters(params.loss_rate, params.rtt);
   if (rates_have_changed) {
-    uint32_t target_bitrate_kbps = (params.target_bitrate + 500) / 1000;
-    encoder_->SetRates(target_bitrate_kbps, params.input_frame_rate);
+    encoder_->SetRateAllocation(params.target_bitrate, params.input_frame_rate);
   }
 }