This is a bug found in automated tab mirroring testing.

The issue is on the hp_i7_640lm_intelhd_win7 machine
Tab mirroring smoothness scores are consistently ~20
Tab mirroring freezing scores are consistently ~78
The scores have been low for a long time. The scores were also low in Sept '17, which is the oldest data point we have in gcs.

Refer to the internal cv perf dashboard for more data points and gcs links.