[MD settings] using h2 for sub-headers consistently.
This CL switches several differently styled sub-headers to all use h2
tags. This is good because it makes them all consistent and h2 is a good
choice because screen readers may scan for h2 tags specifically to give
the user context about what is on the screen.
BUG=
638461
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
Committed:
https://crrev.com/a56e76de0f7e38f81f5be072f98a44516124b8bd
Cr-Commit-Position: refs/heads/master@{#414621}