fix truncate call to use extension method

lib/runtime/dart/_interceptors.js

Index: lib/runtime/dart/_interceptors.js
diff --git a/lib/runtime/dart/_interceptors.js b/lib/runtime/dart/_interceptors.js
index 9e852c8eb2d3c975e06fc71cc3d84f174be900d1..bfd65840cca1ffb0df62a081b00f64b8a5d38977 100644
--- a/lib/runtime/dart/_interceptors.js
+++ b/lib/runtime/dart/_interceptors.js
@@ -918,7 +918,7 @@ dart_library.library('dart/_interceptors', null, /* Imports */[
     get [dartx.bitLength]() {
       let nonneg = dart.notNull(this[dartx['<']](0)) ? dart.notNull(this[dartx['unary-']]()) - 1 : this;
       if (dart.notNull(nonneg) >= 4294967296) {
-        nonneg = (dart.notNull(nonneg) / 4294967296).truncate();
+        nonneg = (dart.notNull(nonneg) / 4294967296)[dartx.truncate]();
         return dart.notNull(JSInt._bitCount(JSInt._spread(nonneg))) + 32;
       }
       return JSInt._bitCount(JSInt._spread(nonneg));