fix truncate call to use extension method

lib/runtime/dart/_isolate_helper.js

 dart_library.library('dart/_isolate_helper', null, /* Imports */[
   "dart_runtime/dart",
   'dart/core',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/isolate',
   'dart/_foreign_helper',
   'dart/collection',
   'dart/async'
 ], /* Lazy imports */[
@@ skipping 1504 matching lines @@
   dart.fn(hasTimer, core.bool, []);
   class CapabilityImpl extends core.Object {
     CapabilityImpl() {
       this._internal(_js_helper.random64());
     }
     _internal(id) {
       this[_id] = id;
     }
     get hashCode() {
       let hash = this[_id];
-      hash = dart.notNull(hash) >> 0 ^ (dart.notNull(hash) / 4294967296).truncate();
+      hash = dart.notNull(hash) >> 0 ^ (dart.notNull(hash) / 4294967296)[dartx.truncate]();
       hash = ~dart.notNull(hash) + (dart.notNull(hash) << 15) & 4294967295;
       hash = dart.notNull(hash) ^ dart.notNull(hash) >> 12;
       hash = dart.notNull(hash) * 5 & 4294967295;
       hash = dart.notNull(hash) ^ dart.notNull(hash) >> 4;
       hash = dart.notNull(hash) * 2057 & 4294967295;
       hash = dart.notNull(hash) ^ dart.notNull(hash) >> 16;
       return hash;
     }
     ['=='](other) {
       if (dart.notNull(core.identical(other, this)))
@@ skipping 18 matching lines @@
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 });