Stop deferring commits on body tag insertion if there are no pending stylesheet loads.

At that point we can be fairly sure we'll have something accurate to paint soon, and eliminates long delays on first paint for pages that don't otherwise force any layouts until much later (like gws).

The linked bug has performance numbers, but note that there's a possibility this may regress zero-latency (i.e. no netsim) page cycler times. The tradeoff is well worth it however.

R=jamesr@chromium.org
BUG=344537

Review URL: https://codereview.chromium.org/157963002

git-svn-id: svn://svn.chromium.org/blink/trunk@167465 bbb929c8-8fbe-4397-9dbb-9b2b20218538