Add comment support to the Media Query tokenizer

The Media query tokenizer did not support CSS comments which isn't compliant with the CSS syntax spec, and is a regression.
This CL fixes that.

BUG=357969

Review URL: https://codereview.chromium.org/218323003

git-svn-id: svn://svn.chromium.org/blink/trunk@170421 bbb929c8-8fbe-4397-9dbb-9b2b20218538