Moved console.profile/profileEnd implementation into InspectorProfilerAgent

This allowed to delete InspectorInstrumentation::profilerEnabled and InspectorInstrumentation::getUserInitiatedProfileName. It is now hanled inside the agent. The agent is available to the instrumentation when front-end is connected and Profiler domain was enabled.

drive-by: addProfile methods in the agent that had single call site

BUG=327298
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/114153002

git-svn-id: svn://svn.chromium.org/blink/trunk@163845 bbb929c8-8fbe-4397-9dbb-9b2b20218538