Remove virtual destructor from WorkerSettings, and make the constructor explicit.

It has no base or derived classes, so its destructor need not be declared virtual.

It has a one-argument constructor, which per the style guide should be declared
'explicit' to avoid undesired implicit conversions.

Review-Url: https://codereview.chromium.org/2186663002
Cr-Commit-Position: refs/heads/master@{#407922}
1 file changed