Create minified sources for wtb benchmarks #825

Job	Run time
Test Build	1m 30s
Test Browser on macOS (safari, disabled)	2m 14s
Test Browser on macOS (safari, main)	1m 6s
Test Browser on macOS (safari, default)	3m 16s
Test Browser on Linux (chrome, default)	1m 4s
Test Browser on Linux (firefox, default)	1m 15s
Test Browser on Linux (chrome, main)	35s
Test Browser on Linux (chrome, disabled)	1m 0s
Test Shell (spidermonkey, main)	48s
Test Browser on Linux (firefox, disabled)	1m 15s
Test Shell (spidermonkey, default)	4m 32s
Test Shell (jsc, default)	1m 42s
Test Browser on Linux (firefox, main)	51s
Test Shell (v8, default)	2m 27s
Test Shell (jsc, main)	45s
Test Shell (v8, main)	35s
Test Shell (v8, disabled)	1m 31s
Test Shell (spidermonkey, disabled)	1m 50s
Test Shell (jsc, disabled)	1m 35s
	29m 51s

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