Make profiling lock global rather than per Target

We should pause any actions that could affect performance if any of the targets is being profiled, not only current target.

BUG=403684
R=sergeyv@chromium.org

Review URL: https://codereview.chromium.org/475803002

git-svn-id: svn://svn.chromium.org/blink/trunk@180336 bbb929c8-8fbe-4397-9dbb-9b2b20218538