DCHECK that hostname is not empty in MarkAlternativeServiceBroken.

DCHECK that hostname is not empty in MarkAlternativeServiceBroken.

The concept of brokenness for alternative services has been decoupled from the
origin to alternative service mapping.  MarkAlternativeServiceBroken marks an
actual alternative service broken by itself, not in relation to any particular
origin.  Therefore callers are expected to pass an alternative service with a
non-empty hostname.  (Empty hostnames are only used in the mapping to signify
"default host", which is relevant when alternative services of a canonical host
is used for other origins.)  This CL adds a DCHECK to document that.

BUG=392575
Committed: https://crrev.com/37a0555d240f511282260f77a1b694b407b07198
Cr-Commit-Position: refs/heads/master@{#336123}

[Bence, 2015-06-24 20:30:48]

bnc@chromium.org changed reviewers:
+ rch@chromium.org

[Bence, 2015-06-24 20:30:48]

Ryan: PTAL.  Thanks.

[Ryan Hamilton, 2015-06-24 21:09:45]

lgtm

[Bence, 2015-06-25 11:16:23]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2015-06-25 11:16:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1203233002/1

[commit-bot: I haz the power, 2015-06-25 11:20:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-25 11:22:02]

Patchset 1 (id:??) landed as
https://crrev.com/37a0555d240f511282260f77a1b694b407b07198
Cr-Commit-Position: refs/heads/master@{#336123}