Revert 165858 "Send HeapProfiler.enable only when profiles panel..."

> Send HeapProfiler.enable only when profiles panel is shown
> 
> Otherwise on cross-process navigation we get following console error:
> 
> [22766:22766:0127/193003:ERROR:CONSOLE(237)] "Protocol Error: the message HeapProfiler.resetProfiles is for non-existing domain 'HeapProfiler'", source: chrome-devtools://devtools/bundled/InspectorBackend.js (237)
> 
> BUG=None
> R=alph@chromium.org
> 
> Review URL: https://codereview.chromium.org/132903010

TBR=yurys@chromium.org

Review URL: https://codereview.chromium.org/142863007

git-svn-id: svn://svn.chromium.org/blink/trunk@165866 bbb929c8-8fbe-4397-9dbb-9b2b20218538