Skip feature detection in shim mode (#549) #1077

Job	Run time
Check Formatting	20s
Firefox Browser Tests (67.0)	3m 18s
Chrome Browser Tests (695071)	2m 6s
Firefox Browser Tests (108.0)	3m 26s
Firefox Browser Tests (latest)	3m 26s
Chrome Browser Tests (913920)	2m 44s
Chrome Browser Tests (latest)	3m 16s
Firefox Browser Tests (89.0)	3m 27s
Chrome Browser Tests (1408499)	2m 5s
Chrome Browser Tests (1306171)	2m 5s
Firefox Browser Tests (126.0)	3m 35s
Chrome Browser Tests (859178)	2m 0s
	31m 48s

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