Fix compilation failure on Win64 since r14020.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/12989002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14035 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix isolate getter in DebugAgent

Review URL: https://codereview.chromium.org/12678015

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14036 ce2b1a6d-e550-0410-aec6-3dcde31c8c00