Add explanatory text to help translate 'Host'.
Add explanatory text to help translate 'Host'.

We've had a request from our translators to disambiguate these strings.

BUG=b/24592063, b/24595057

Review URL: https://codereview.chromium.org/1402473003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#353425}

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