Adjust memory limits.

- Introduce new constant: kBootCodeSizeMultiplier to handle the code size differences across the platforms.

- Increase memory limits due to larger code size on MIPS.

BUG=
R=danno@chromium.org, plind44@gmail.com

Review URL: https://codereview.chromium.org/234153002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20825 ce2b1a6d-e550-0410-aec6-3dcde31c8c00