Moved MQ parsing block tracking to tokenizer

For better spec compliance of the tokenizer itself, and to enable the sizes
parser to be aware of blocks, I've moved the block tracking logic from the 
MQ parser to the tokenizer.

BUG=357586

Review URL: https://codereview.chromium.org/225293006

git-svn-id: svn://svn.chromium.org/blink/trunk@171237 bbb929c8-8fbe-4397-9dbb-9b2b20218538