Made dart2js constructor lookup logic "private"-aware, fixed 4740 bug.

lib/compiler/implementation/universe/universe.dart

Index: lib/compiler/implementation/universe/universe.dart
diff --git a/lib/compiler/implementation/universe/universe.dart b/lib/compiler/implementation/universe/universe.dart
index 3baa353b64a6cb4590542ab0b1d7df70428119af..5dd6a4af6fd86c441ebb3d03ba1d1666ea3450e3 100644
--- a/lib/compiler/implementation/universe/universe.dart
+++ b/lib/compiler/implementation/universe/universe.dart
@@ -186,6 +186,17 @@ class Selector {
       : this(SelectorKind.CALL, Compiler.CALL_OPERATOR_NAME, null,
              selector.argumentCount, selector.namedArguments);
 
+  Selector.callConstructor(SourceString constructorName,
+                           LibraryElement library)
+      : this(SelectorKind.CALL,
+             constructorName,
+             library,
+             0,
+             const []);
+
+  Selector.callDefaultConstructor(LibraryElement library)
+      : this(SelectorKind.CALL, const SourceString(""), library, 0, const []);
+
   // TODO(kasperl): This belongs somewhere else.
   Selector.noSuchMethod()
       : this(SelectorKind.CALL, Compiler.NO_SUCH_METHOD, null, 2);