Cleanup argument mismatch message.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index e5bf8717a8a8bbd75b70d21a30336370c60053ad..3aa2bf4b899686d4ae10bf884186344d0f37b1a2 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -527,6 +527,15 @@ class Elements {
     }
   }
 
+  static String constructorNameForDiagnostics(String className,
+                                              String constructorName) {
+    String classNameString = className;
+    String constructorNameString = constructorName;
+    return (constructorName == '')
+        ? classNameString
+        : "$classNameString.$constructorNameString";
+  }
+
   /// Returns `true` if [name] is the name of an operator method.
   static bool isOperatorName(String name) {
     return name == 'unary-' || isUserDefinableOperator(name);