- when logging 'open-tag' / 'close-tag' events, don't depend on
   FLAG_log (as it may be not enabled, e.g. in Chromium);

 - PauseProfiler / ResumeProfiler were supposing that they
   use 'is_logging_' var exclusively, thus preventing any
   other logging that may be turned on for diagnostic purposes.

Review URL: http://codereview.chromium.org/661246

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3986 ce2b1a6d-e550-0410-aec6-3dcde31c8c00