Don't add Profile/ProfileEnd console messages in profiler agent

These messages will be added on the front-end when corresponding events are handled. This allows to move creation of profile titles to the front-end and simplify back-end.

BUG=327298
R=alph@chromium.org, eustas@chromium.org

Review URL: https://codereview.chromium.org/93933010

git-svn-id: svn://svn.chromium.org/blink/trunk@163954 bbb929c8-8fbe-4397-9dbb-9b2b20218538