Do not add forwarding constructors to a pricate constructor from a different library.

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

Index: sdk/lib/_internal/compiler/implementation/typechecker.dart
diff --git a/sdk/lib/_internal/compiler/implementation/typechecker.dart b/sdk/lib/_internal/compiler/implementation/typechecker.dart
index 522e6c272339b83109853bb7e095671dd3005adb..ad1df28633b19442ea24c7f47a1d9e6d60acec98 100644
--- a/sdk/lib/_internal/compiler/implementation/typechecker.dart
+++ b/sdk/lib/_internal/compiler/implementation/typechecker.dart
@@ -752,7 +752,11 @@ class TypeCheckerVisitor extends Visitor<DartType> {
         }
       }
     }
-    if (!interface.element.isProxy) {
+    // We didn't find a member with the correct name.  If this lookup is for a
+    // super or redirecting initializer, the resolver has already emitted an
+    // error message.  If the target is a proxy, no warning needs to be emitted.
+    // Otherwise, try to emit the most precise warning.
+    if (!interface.element.isProxy && !analyzingInitializer) {
       bool foundPrivateMember = false;
       if (memberName.isPrivate) {
         void findPrivateMember(MemberSignature member) {