Fix for issue 2468: also convert Dart closures to Js closures in stubs for native methods.

lib/compiler/implementation/native_emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class NativeEmitter {
 
   Compiler compiler;
   StringBuffer buffer;
 
   // Classes that participate in dynamic dispatch. These are the
@@ skipping 121 matching lines @@
 
     if (hasUsedSelectors) classesWithDynamicDispatch.add(classElement);
   }
 
   List<ClassElement> getDirectSubclasses(ClassElement cls) {
     List<ClassElement> result = subtypes[cls];
     if (result === null) result = const<ClassElement>[];
     return result;
   }
 
+  void potentiallyConvertDartClosuresToJs(StringBuffer code,
+                                          FunctionElement member) {
+    FunctionParameters parameters = member.computeParameters(compiler);
+    Element converter =
+        compiler.findHelper(const SourceString('convertDartClosureToJS'));
+    String closureConverter = compiler.namer.isolateAccess(converter);
+    parameters.forEachParameter((Element parameter) {
+      Type type = parameter.computeType(compiler);
+      if (type is FunctionType) {
+        String name = parameter.name.slowToString();
+        code.add('  $name = $closureConverter($name);\n');
+      }
+    });
+  }
+
   void emitParameterStub(Element member,
                          String invocationName,
                          String stubParameters,
                          List<String> argumentsBuffer,
                          int indexOfLastOptionalArgumentInParameters) {
     // The target JS function may check arguments.length so we need to
     // make sure not to pass any unspecified optional arguments to it.
     // For example, for the following Dart method:
     //   foo([x, y, z]);
     // The call:
     //   foo(y: 1)
     // must be turned into a JS call to:
     //   foo(null, y).
 
     List<String> nativeArgumentsBuffer = argumentsBuffer.getRange(
         0, indexOfLastOptionalArgumentInParameters + 1);
 
     ClassElement classElement = member.enclosingElement;
     String nativeName = classElement.nativeName.slowToString();
     String nativeArguments = Strings.join(nativeArgumentsBuffer, ",");
 
+    StringBuffer code = new StringBuffer();
+    potentiallyConvertDartClosuresToJs(code, member);
+
     String name = member.name.slowToString();
-    String code = '  return this.$name($nativeArguments);\n';
+    code.add('  return this.$name($nativeArguments);');
+
     if (isNativeLiteral(nativeName) || !overriddenMethods.contains(member)) {
       // Call the method directly.
-      buffer.add(code);
+      buffer.add(code.toString());
     } else {
       native.generateMethodWithPrototypeCheck(
-          compiler, buffer, invocationName, code, stubParameters);
+          compiler, buffer, invocationName, code.toString(), stubParameters);
     }
   }
 
   void emitDynamicDispatchMetadata() {
     if (classesWithDynamicDispatch.isEmpty()) return;
     buffer.add('// ${classesWithDynamicDispatch.length} dynamic classes.\n');
 
     // Build a pre-order traversal over all the classes and their subclasses.
     Set<ClassElement> seen = new Set<ClassElement>();
     List<ClassElement> classes = <ClassElement>[];
@@ skipping 153 matching lines @@
     String toStringName = compiler.namer.instanceMethodName(
         null, const SourceString('toString'), 0);
     objectProperties.add("$defPropName(Object.prototype, '$toStringName', ");
     objectProperties.add(
         'function() { return $toStringHelperName(this); });\n');
 
     // Finally, emit the code in the main buffer.
     targetBuffer.add('(function() {\n$objectProperties$buffer\n})();\n');
   }
 }