Cleanup useless parameter object_is_smi for NumberToStringStub::GenerateLookupNumberStringCache().

object_is_smi was always false so there's no need to actually have it.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/19541007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15774 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Cleanup StringAddFlags.

Avoid duplication of StringAddFlags in the platform specific code stubs header files.
Fix the inverted flag logic, replacing it with a scheme that is easier to understand.

Depends on: https://codereview.chromium.org/19541003

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/19492006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15775 ce2b1a6d-e550-0410-aec6-3dcde31c8c00