Initialize forgotten Isolate member.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/23769008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16613 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix MSVC compiler warning after commit r16612.

TBR=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/23534052

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16614 ce2b1a6d-e550-0410-aec6-3dcde31c8c00