ES6 spec intentionally drops the WeakMap#clear to allow engine to implement WeakMap as a per-object table.
Created attachment 253973 [details] Patch
For reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap/clear indicates that clear() "part of the ECMAScript 6 draft specification until revision 28 (version of October 14, 2014), but has been removed in later versions of the draft. It will not be part of the final standard.” Firefox 38.0.1 still supports it. Chrome 43.0.2357.81 has removed it.
Comment on attachment 253973 [details] Patch Thank you for your review and reference.
Comment on attachment 253973 [details] Patch Clearing flags on attachment: 253973 Committed r185041: <http://trac.webkit.org/changeset/185041>
All reviewed patches have been landed. Closing bug.