Entering debugger scope should not make debugger active.

The motivation is that by only entering the debugger scope to call into
the debug context should not cause code to be compiled for debugging.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/306563002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21645 ce2b1a6d-e550-0410-aec6-3dcde31c8c00