nameInThis() in oop.js is slow

[ajklein]

The code is reproduced below:

function nameInThis(inValue) {
  for (var n in this) {
    var d = getPropertyDescriptor(this, n);
    if (d.value == inValue) {
      return n;
    }
  }
}

When this hits an HTML element, it ends up walking through all kinds of problematic properties, like offsetTop and isContentEditable, which then show up very hot on a profile.

[sjmiles]

As of 2d5f89b, prototypes registered via Polymer are name hinted so they will never call nameInThis.

Also, fwiw, nameInThis was optimized in 26e8b14, even though only edge cases that should ever get there.