Use Object.create instead of a tmp-function.

dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart

Index: dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart
diff --git a/dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart b/dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart
index c6fd99a3343874b392017126c23958e90c0ebb30..2de11198c0b566024fabc4e4135d624ee2fd2d9a 100644
--- a/dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart
+++ b/dart/sdk/lib/_internal/compiler/js_lib/js_helper.dart
@@ -1970,7 +1970,6 @@ abstract class Closure implements Function {
     // So we only use the new instance to access the constructor property and
     // use Object.create to create the desired prototype.
     var prototype = isStatic
-        // TODO(ahe): Safe to use Object.create?
         ? JS('TearOffClosure', 'Object.create(#.constructor.prototype)',
              new TearOffClosure())
         : JS('BoundClosure', 'Object.create(#.constructor.prototype)',
@@ -1986,7 +1985,8 @@ abstract class Closure implements Function {
                      '"this.\$initialize(a,b,c,d);"+#)',
                  functionCounter++);
 
-    // TODO(ahe): Is it necessary to set the constructor property?
+    // It is necessary to set the constructor property, otherwise it will be
+    // "Object".
     JS('', '#.constructor = #', prototype, constructor);
 
     JS('', '#.prototype = #', constructor, prototype);