Create minified sources for wtb benchmarks #828

Job	Run time
Test Build	1m 37s
Test Browser on macOS (safari, disabled)	1m 55s
Test Browser on macOS (safari, default)	2m 36s
Test Browser on Linux (chrome, main)	43s
Test Browser on Linux (firefox, disabled)	1m 53s
Test Browser on Linux (firefox, main)	1m 32s
Test Browser on Linux (chrome, default)	58s
Test Browser on macOS (safari, main)	49s
Test Browser on Linux (firefox, default)	2m 1s
Test Shell (spidermonkey, main)	50s
Test Shell (jsc, default)	3m 3s
Test Shell (jsc, main)	43s
Test Shell (jsc, disabled)	1m 50s
Test Shell (v8, main)	44s
Test Shell (spidermonkey, default)	4m 54s
Test Browser on Linux (chrome, disabled)	1m 1s
Test Shell (v8, disabled)	1m 31s
Test Shell (spidermonkey, disabled)	1m 58s
Test Shell (v8, default)	3m 20s
	33m 58s

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