dashboard/app: show manager unique coverage #15038

Job	Run time
aux	4m 54s
arch (presubmit_arch_linux)	10m 58s
arch (presubmit_arch_freebsd)	6m 33s
arch (presubmit_arch_netbsd)	4m 27s
arch (presubmit_arch_openbsd)	4m 23s
build	3m 52s
arch (presubmit_arch_darwin)	4m 28s
arch (presubmit_arch_windows)	3m 28s
arch (presubmit_arch_executor)	3m 15s
dashboard	3m 36s
gvisor	5m 19s
old	6m 45s
race	8m 29s
race_dashboard	3m 29s
	1h 13m 56s

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