Don't release HTMLToken::m_data's storage between tokens

This was causing us to thrash malloc when parsing documents
which had text-nodes larger than 256 characters.

This drops another 4% off of the benchmark.

BUG=356292

Review URL: https://codereview.chromium.org/217833003

git-svn-id: svn://svn.chromium.org/blink/trunk@170396 bbb929c8-8fbe-4397-9dbb-9b2b20218538