Do not break in native code (including non-builtin debugger code).

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/300773002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21520 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Add defensive assert against a weak callback on an empty persistent.

(This shouldn't happen in the first place, as by definition that callback would never be called. However, the referenced bug sorta looks like this happened. If so, the CHECK should help us pinpoint the culprit.)

R=jochen@chromium.org
BUG=368095
LOG=N

Review URL: https://codereview.chromium.org/265823006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00