Accept PWS results without a results key

Accept PWS results without a results key

The Physical Web Service should not have to send a results key if there
are no results (and it currently doesn't).  This change does a better
job of tolerating such responses.

BUG=556988
Committed: https://crrev.com/c9a1c0c7453645ae1e800749e0d44cec4bbf7c25
Cr-Commit-Position: refs/heads/master@{#361393}

[conleyo, 2015-11-20 22:58:48]

conleyo@google.com changed reviewers:
+ conleyo@google.com, nyquist@chromium.org

[conleyo, 2015-11-20 22:58:48]

+mattreynolds,nyquist

[mmocny, 2015-11-23 16:57:24]

mmocny@chromium.org changed reviewers:
+ mmocny@chromium.org

[mmocny, 2015-11-23 16:57:24]

lgtm

[nyquist, 2015-11-24 09:21:37]

lgtm

[cco3, 2015-11-24 17:55:56]

The CQ bit was checked by cco3@chromium.org

[commit-bot: I haz the power, 2015-11-24 17:56:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1465923004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1465923004/20001

[commit-bot: I haz the power, 2015-11-24 18:36:06]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-24 18:36:49]

Patchset 2 (id:??) landed as
https://crrev.com/c9a1c0c7453645ae1e800749e0d44cec4bbf7c25
Cr-Commit-Position: refs/heads/master@{#361393}