Generalize utilities to allow code templatization

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/17853004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15357 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
The check for internalized strings relied on the fact that we had less
than 64 distinct InstanceTypes. We are hitting that boundary, so this
check needs to be more comprehensive. In fact, two bits need to be
tested: verify that kNotStringTag isn't set, and that kInternalizedTag
is set.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/17895002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15358 ce2b1a6d-e550-0410-aec6-3dcde31c8c00