GetActiveProfilerModules()/PauseProfiler()/ResumeProfiler() can be reached
from the API when the --prof runtime flag is not set, leading to null
dereferences. Verify that Logger::profiler_ is non-NULL before using it.

Review URL: http://codereview.chromium.org/2843023

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4953 ce2b1a6d-e550-0410-aec6-3dcde31c8c00