Add a non-trivial CSS parsing performance test.

All of the rest of our CSS tests use very tiny stylesheets.

This uses Twitter's popular (and compatibly licensed) CSS
framework "bootstrap" and parses it in a runs-per-second test.

We hit about 150 runs/s vs. FF's 180 runs/s on this test.

The top symbol (with 30% of total time) is cssyyparse.
Lots of room to optimize here.

BUG=330389
NOTRY=true

Review URL: https://codereview.chromium.org/120643002

git-svn-id: svn://svn.chromium.org/blink/trunk@164304 bbb929c8-8fbe-4397-9dbb-9b2b20218538