Fix indentation and formatting for [DoNotCheckSecurity] in code_generator_v8.pm

* Fix confusingly incorrect indentation
* Replace long sequence of appends with heredoc

Review URL: https://codereview.chromium.org/61723005

git-svn-id: svn://svn.chromium.org/blink/trunk@161496 bbb929c8-8fbe-4397-9dbb-9b2b20218538