Bug 1259172 - Fix assertion in Codegen.py's InitUnforgeablePropertiesOnHolder function. r=bz

dom/bindings/Codegen.py

@@ -3397,7 +3397,7 @@ def InitUnforgeablePropertiesOnHolder(descriptor, properties, failureCode):
     assert (properties.unforgeableAttrs.hasNonChromeOnly() or
             properties.unforgeableAttrs.hasChromeOnly() or
             properties.unforgeableMethods.hasNonChromeOnly() or
-            properties.unforgeableMethods.hasChromeOnly)
+            properties.unforgeableMethods.hasChromeOnly())
 
     unforgeables = []