Prevent liveedit on or under generators with open activations

R=yangguo@chromium.org
LOG=N
TEST=mjsunit/harmony/generators-debug-liveedit.js
BUG=

Review URL: https://codereview.chromium.org/266983004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21174 ce2b1a6d-e550-0410-aec6-3dcde31c8c00