1. Global{Context,Scope}=>Script{Context,Scope}
2. Enable fixed tests
3. Update comments

R=rossberg@chromium.org
BUG=v8:2198
LOG=N

Review URL: https://codereview.chromium.org/716833002

Cr-Commit-Position: refs/heads/master@{#25291}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25291 ce2b1a6d-e550-0410-aec6-3dcde31c8c00