Log uses of isolate archive and exparchive when 'chromium' build tag is set.

client/cmd/isolate/common.go

Index: client/cmd/isolate/common.go
diff --git a/client/cmd/isolate/common.go b/client/cmd/isolate/common.go
index ba0da5b712177523bea62a8b9bfa0ef0a3b8b802..8c96d2916f9fac1933d210d132d5b6d31e753425 100644
--- a/client/cmd/isolate/common.go
+++ b/client/cmd/isolate/common.go
@@ -135,6 +135,12 @@ type loggingFlags struct {
 	EventlogEndpoint string
 }
 
+const eventlogEndpointHelp = `The URL destination for eventlogs. The following special values are supported:
+\t"prod": use the prod eventlog endpoint
+\t"test": use the test eventlog endpoint
+\t"none": disable eventlogging
+\t"auto": use the prod endpoint if --isolate-server is set to the prod isolate server; otherwise disable eventlogging.`
+
 func (lf *loggingFlags) Init(f *flag.FlagSet) {
-	f.StringVar(&lf.EventlogEndpoint, "eventlog-endpoint", "", `The URL destination for eventlogs. The special values "prod" or "test" may be used to target the standard prod or test urls repspectively. An empty string disables eventlogging.`)
+	f.StringVar(&lf.EventlogEndpoint, "eventlog-endpoint", "auto", eventlogEndpointHelp)

[tandrii(chromium), 2017/06/06 07:14:48]

IMO, this should default to None, while recipe invocation on our bots should
explicitly state auto or maybe even just list prod.

This will be inline with other tooling that developers may directly or
indirectly invoke on their workstations.

 }