Do not log DNS resolution entries from NQE in the netlog

Currently, when Network Quality Estimator (NQE) resolves
a DNS address, the details of it are logged into the
netlog. This is unnecessary, and adds noise.

The CL provides an empty NetLogWithSource to the
host resolver to prevent logging.

Bug: 731797
Change-Id: I6fd6c8529b3766dfd3c777c52bfcbc63e0a911b7
Reviewed-on: https://chromium-review.googlesource.com/557819
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484353}

• net/nqe/network_quality_estimator.cc[diff]
• net/nqe/network_quality_estimator_util.cc[diff]
• net/nqe/network_quality_estimator_util.h[diff]
• net/nqe/network_quality_estimator_util_unittest.cc[diff]
• net/nqe/throughput_analyzer.cc[diff]
• net/nqe/throughput_analyzer_unittest.cc[diff]