Unload debugger on isolate deinit.

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18682003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Refactored code a bit to improve StringReplace performance

1. Use inline macro to mitigate the side effect emulation overhead
2. Refactor Zone::DeleteAll() to merge two loops together

R=bmeurer@chromium.org, yangguo@chromium.org

Review URL: https://codereview.chromium.org/18057004

Patch from Weiliang Lin <weiliang.lin2@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15522 ce2b1a6d-e550-0410-aec6-3dcde31c8c00