Fixes #479

lib/runtime/dart/_runtime.js

 dart_library.library('dart/_runtime', null, /* Imports */[
 ], /* Lazy imports */[
   'dart/core',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/async',
   'dart/collection'
 ], function(exports, core, _interceptors, _js_helper, async, collection) {
   'use strict';
   function mixin(base, ...mixins) {
@@ skipping 73 matching lines @@
   }
   function getGenericArgs(type) {
     return safeGetOwnProperty(type, _typeArguments);
   }
   const _constructorSig = Symbol("sigCtor");
   const _methodSig = Symbol("sig");
   const _staticSig = Symbol("sigStatic");
   function getMethodType(obj, name) {
     if (obj === void 0) return void 0;
     if (obj == null) return void 0;
-    let sigObj = obj.__proto__.constructor[_methodSig];
+    return getMethodTypeFromType(obj.__proto__.constructor, name);
+  }
+  function getMethodTypeFromType(type, name) {
+    let sigObj = type[_methodSig];
     if (sigObj === void 0) return void 0;
     let parts = sigObj[name];
     if (parts === void 0) return void 0;
     return definiteFunctionType.apply(null, parts);
   }
   function classGetConstructorType(cls, name) {
     if (!name) name = cls.name;
     if (cls === void 0) return void 0;
     if (cls == null) return void 0;
     let sigCtor = cls[_constructorSig];
@@ skipping 838 matching lines @@
           if (i > 0) name += ', ';
           name += typeName(args[i]);
         }
         name += '>';
       }
       return name;
     }
     if (tag) return "Not a type: " + tag.name;
     return "JSObject<" + type.name + ">";
   }
+  function getImplicitFunctionType(type) {
+    if (isFunctionType(type)) return type;
+    return getMethodTypeFromType(type, 'call');
+  }
   function isFunctionType(type) {
     return type instanceof AbstractFunctionType || type == core.Function;
   }
   function isFunctionSubType(ft1, ft2) {
     if (ft2 == core.Function) {
       return true;
     }
     let ret1 = ft1.returnType;
     let ret2 = ft2.returnType;
     if (!isSubtype_(ret1, ret2)) {
@@ skipping 78 matching lines @@
     if (t1 == t2) return true;
     if (_isTop(t2) || _isBottom(t1)) {
       return true;
     }
     if (_isTop(t1) || _isBottom(t2)) {
       return false;
     }
     if (isClassSubType(t1, t2)) {
       return true;
     }
+    t1 = getImplicitFunctionType(t1);
+    if (!t1) return false;
     if (isFunctionType(t1) && isFunctionType(t2)) {
       return isFunctionSubType(t1, t2);
     }
     return false;
   }
   function isClassSubType(t1, t2) {
     t1 = canonicalType(t1);
     assert_(t2 == canonicalType(t2));
     if (t1 == t2) return true;
     if (t1 == core.Object) return false;
@@ skipping 143 matching lines @@
   const global_ = typeof window == "undefined" ? global : window;
   const JsSymbol = Symbol;
   // Exports:
   exports.mixin = mixin;
   exports.getMixins = getMixins;
   exports.getImplements = getImplements;
   exports.generic = generic;
   exports.getGenericClass = getGenericClass;
   exports.getGenericArgs = getGenericArgs;
   exports.getMethodType = getMethodType;
+  exports.getMethodTypeFromType = getMethodTypeFromType;
   exports.classGetConstructorType = classGetConstructorType;
   exports.bind = bind;
   exports.setSignature = setSignature;
   exports.hasMethod = hasMethod;
   exports.virtualField = virtualField;
   exports.defineNamedConstructor = defineNamedConstructor;
   exports.getExtensionType = getExtensionType;
   exports.dartx = dartx;
   exports.getExtensionSymbol = getExtensionSymbol;
   exports.defineExtensionNames = defineExtensionNames;
@@ skipping 64 matching lines @@
   exports.JSObject = JSObject;
   exports.jsobject = jsobject;
   exports.AbstractFunctionType = AbstractFunctionType;
   exports.FunctionType = FunctionType;
   exports.Typedef = Typedef;
   exports.functionType = functionType;
   exports.definiteFunctionType = definiteFunctionType;
   exports.typedef = typedef;
   exports.isDartType = isDartType;
   exports.typeName = typeName;
+  exports.getImplicitFunctionType = getImplicitFunctionType;
   exports.isFunctionType = isFunctionType;
   exports.isFunctionSubType = isFunctionSubType;
   exports.canonicalType = canonicalType;
   exports.subtypeMap = subtypeMap;
   exports.isSubtype = isSubtype;
   exports.isSubtype_ = isSubtype_;
   exports.isClassSubType = isClassSubType;
   exports.isGroundType = isGroundType;
   exports.defineProperty = defineProperty;
   exports.getOwnPropertyDescriptor = getOwnPropertyDescriptor;
@@ skipping 12 matching lines @@
   exports.copyProperties = copyProperties;
   exports.export = export_;
   exports.defineLazyClass = defineLazyClass;
   exports.defineLazyProperties = defineLazyProperties;
   exports.defineLazyClassGeneric = defineLazyClassGeneric;
   exports.as = as_;
   exports.is = is_;
   exports.global = global_;
   exports.JsSymbol = JsSymbol;
 });