Can not expand native JS objects in Dart DevTools

When stopped at a breakpoint, you can't expand a variable that represents a native JS object. For example `DcoumentFragment`. We should either not enable the expansion of this variable as to not confuse users or actually display the JS properties.

Reproduce the issue in Dart DevTools by stopping at a breakpoint with a variable representing a native JavaScript object such as DocumentFragment. Trace the variable expansion behavior; done means native objects no longer appear expandable unless their JavaScript properties can actually be displayed.

Written by the indexing model from the issue text.