Prevent grokdump from crying about invalid input.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/14660012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14572 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
deprecate Context::New which returns Persistent

BUG=
TBR=marja@chromium.org

Review URL: https://codereview.chromium.org/14793004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14573 ce2b1a6d-e550-0410-aec6-3dcde31c8c00