The Chestnut Hill Mall, or the Mall at Chestnut Hill as it is officially called, is part of Newton, not Boston. Newton, it's own city, was incorporated in 1688.
Interestingly, Newton was never part of Boston, but rather was originally part of Cambridge. Now, Newton doesn't even border Cambridge - go figure! Newton is not named after Isaac Newton, who was a great physicist and mathematician.
<pseudo-science rant>Isaac Newton's greatest contribution to science was his laws of motion. He derived the equation F=ma. This equation is essentially meaningless because it is dependent upon time, so it is meaningless as one approaches the speed of light and is no longer experiencing time in a linear fashion.</pseudo-science rant>
Newton is actually derived from New Towne, and shortened and American-ized into Newton. Speaking of America, the Hammond Pond, which is right next to The Mall at Chestnut Hill at New Towne would be a perfect place to hold Olympic Swimming in 2024. The Olympics will enable us to convert the Green Line into HRT. There can be ferries to and from a relocated Chestnut Hill stop - and the "Olympic Village at the Mall at Chestnut Hill at New Towne in Linear Time Space"