Follows-up 42c97fa (I82ed4ade), 63c5943a9 (Ic71346196).
This commit makes no functional changes, but it reduces overhead
from the SyntaxHighlight code when interacting with other features,
such as elaborate modals or other hashchange-heavy code paths that
a gadget might produce.
It uses vanilla DOM instead of jQuery where possible, and adds an
early return rather than fairly deep continuation no-ops.
Change-Id: I2264f6f398193802f05c738bad4c294da007fb27
The 'hll' CSS only targets the .linenos selector, but it doesn't
hurt to avoid unnecessary DOM changes.
Change-Id: Ic7134619606c6e4abc2480ddc9650d0352fc33da
