Unified the structure of VirtualMemory implementations across platforms a bit.

This is just shuffling some code around to make comparing the platform files easier.

Made cygwin/nullos support a bit more complete on the way.

Review URL: https://codereview.chromium.org/14162004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14250 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Turn off pre-tenuring of fast literals when we turn off high promotion mode.

BUG=

Review URL: https://codereview.chromium.org/14199003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14251 ce2b1a6d-e550-0410-aec6-3dcde31c8c00