Promise.all and Promise race should use "then" rather than "chain".

As specified, they should unwrap resolution values recursively.

BUG=347427
LOG=Y
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/181613006

Patch from Yutaka Hirano <yhirano@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19752 ce2b1a6d-e550-0410-aec6-3dcde31c8c00