DevTools: disable debugger when a profiler is active.

this is the first patch. It does only disable debugger if an experiment settings is on.
In the following patches will block panel from switching.


BUG=

Review URL: https://codereview.chromium.org/335403003

git-svn-id: svn://svn.chromium.org/blink/trunk@176324 bbb929c8-8fbe-4397-9dbb-9b2b20218538