Fix perf regression in screenshare temporal layer bitrate allocation

webrtc/modules/video_coding/codecs/vp8/screenshare_layers_unittest.cc

 /*
  *  Copyright (c) 2013 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 400 matching lines @@
               ElementsAre(kTl0_kbps));
   EXPECT_TRUE(layers_->UpdateConfiguration(&cfg));
 
   EXPECT_EQ(static_cast<uint32_t>(kTl1_kbps), cfg.rc_target_bitrate);
 }
 
 TEST_F(ScreenshareLayerTest, EncoderDrop) {
   ConfigureBitrates();
   CodecSpecificInfoVP8 vp8_info;
   vpx_codec_enc_cfg_t cfg = GetConfig();
+  // Updates cfg with current target bitrate.
+  EXPECT_TRUE(layers_->UpdateConfiguration(&cfg));
 
   uint32_t timestamp = RunGracePeriod();
   timestamp = SkipUntilTl(0, timestamp);
 
   // Size 0 indicates dropped frame.
   layers_->FrameEncoded(0, timestamp, kDefaultQp);
   timestamp += kTimestampDelta5Fps;
   EXPECT_FALSE(layers_->UpdateConfiguration(&cfg));
   EXPECT_EQ(ScreenshareLayers::kTl0Flags, layers_->EncodeFlags(timestamp));
   layers_->PopulateCodecSpecific(false, &vp8_info, timestamp);
@@ skipping 138 matching lines @@
             metrics::NumEvents("WebRTC.Video.Screenshare.Layer1.TargetBitrate",
                                kDefaultTl1BitrateKbps));
 }
 
 TEST_F(ScreenshareLayerTest, AllowsUpdateConfigBeforeSetRates) {
   vpx_codec_enc_cfg_t cfg = GetConfig();
   EXPECT_FALSE(layers_->UpdateConfiguration(&cfg));
 }
 
 }  // namespace webrtc