turn the extensions gallery into HTML
removed empty section tags that were not even nested correctly. didnt seem to be used for anything
Removed duplicate protocols in webstore links
Updated heading for remote debug protocol v 1.1
Updated out-of-date anchor link.
Minor HTML markup edits.

UI elements should be in <b> not <code>
Wrapped YouTube videos in a .video-container so they can be responsive.

Dependent on CL 291663002 (https://codereview.chromium.org/291663002/#ps100001) going through.
Got rid of max-width so <img> can be responsive.