Added inline caching for calls to a field to X64.  Changed a use of Array::kHeaderSize to FixedArray::kHeaderSize on all platforms.
Review URL: http://codereview.chromium.org/149798

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2496 ce2b1a6d-e550-0410-aec6-3dcde31c8c00