Bug 1759324 - fix vp8 under/overshoot percentages r=bryce

This was changed in
https://hg.mozilla.org/mozilla-central/rev/3153ea8804088b11769353a828b1aeb276bdd69b

libvpx became more restrictive about these values here:
https://chromium-review.googlesource.com/c/webm/libvpx/+/2844345/2/vp8/vp8_cx_iface.c

Reset these to the original values which are the same ones used in WebRTC

Differential Revision: https://phabricator.services.mozilla.com/D142528

dom/media/encoder/VP8TrackEncoder.cpp

@@ -116,10 +116,10 @@ nsresult CreateEncoderConfig(int32_t aWidth, int32_t aHeight,
   // ffmpeg doesn't currently support streams that use resize.
   // Therefore, for safety, we should turn it off until it does.
   config->rc_resize_allowed = 0;
-  // Allows 10% under target bitrate to compensate for prior overshoot
-  config->rc_undershoot_pct = 200;
-  // Allows 1.5% over target bitrate to compensate for prior undershoot
-  config->rc_overshoot_pct = 200;
+  // Allows 100% under target bitrate to compensate for prior overshoot
+  config->rc_undershoot_pct = 100;
+  // Allows 15% over target bitrate to compensate for prior undershoot
+  config->rc_overshoot_pct = 15;
   // Tells the decoding application to buffer 500ms before beginning playback
   config->rc_buf_initial_sz = 500;
   // The decoding application will try to keep 600ms of buffer during playback