Move global pretenuring flag check to ShouldGloballyPretenure().

BUG=

Review URL: https://codereview.chromium.org/15734007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14763 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
de-isolate Persistent::Dispose

R=svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/15648008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14764 ce2b1a6d-e550-0410-aec6-3dcde31c8c00