Make DescriptorArray::IsMoreGeneralThan() and DescriptorArray::Merge() compatible again.

BUG=365172
LOG=y
TEST=mjsunit/regress/regress-365172-[1-3]
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/255513005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20922 ce2b1a6d-e550-0410-aec6-3dcde31c8c00