crbug.com/701894 updated the Linux sysroot, making more C++11 features
available. These features include std::map::emplace, making the
corresponding warning the styleguide obsolete.

R=danakj@chromium.org,jbroman@chromium.org
CC=pkasting@chromium.org
BUG=NONE

Review-Url: https://codereview.chromium.org/2844443002
Cr-Commit-Position: refs/heads/master@{#466987}