Fix perf regression in screenshare temporal layer bitrate allocation

webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.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.
 */
 
 #include <stdlib.h>
@@ skipping 161 matching lines @@
       bitrates.push_back(static_cast<uint32_t>(layer_bitrate + 0.5));
     }
     new_bitrates_kbps_ = rtc::Optional<std::vector<uint32_t>>(bitrates);
 
     // Allocation table is of aggregates, transform to individual rates.
     uint32_t sum = 0;
     for (int i = 0; i < num_layers; ++i) {
       uint32_t layer_bitrate = bitrates[i];
       RTC_DCHECK_LE(sum, bitrates[i]);
       bitrates[i] -= sum;
-      sum += layer_bitrate;
+      sum = layer_bitrate;
 
-      if (sum == static_cast<uint32_t>(bitrate_kbps)) {
+      if (sum >= static_cast<uint32_t>(bitrate_kbps)) {
         // Sum adds up; any subsequent layers will be 0.
-        bitrates.resize(i);
+        bitrates.resize(i + 1);
         break;
       }
     }
 
     return bitrates;
   }
 
   bool UpdateConfiguration(vpx_codec_enc_cfg_t* cfg) override {
     if (!new_bitrates_kbps_)
       return false;
@@ skipping 105 matching lines @@
     int simulcast_id,
     int max_temporal_layers,
     uint8_t initial_tl0_pic_idx) const {
   TemporalLayers* tl =
       new RealTimeTemporalLayers(max_temporal_layers, initial_tl0_pic_idx);
   if (listener_)
     listener_->OnTemporalLayersCreated(simulcast_id, tl);
   return tl;
 }
 }  // namespace webrtc