Clean-up v8::ArrayBuffer::Allocator interface

BUG=v8:2823
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/23514050

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Improve alias analysis for HConstants (and fix small snafu in MustAlias).

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/24107003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16651 ce2b1a6d-e550-0410-aec6-3dcde31c8c00