Extend snapshot creation to generate 4-byte values

R=rmcilroy@chromium.org, yangguo@chromium.org

Review URL: https://codereview.chromium.org/623993002

Patch from Andre Baixo <baixo@google.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24401 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'