Fix analyzer's handling of import prefixes not followed by '.'.

tests/language/conditional_method_invocation_test.dart

 // Copyright (c) 2015, 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.
 
 // Verify semantics of the ?. operator when it is used to invoke a method.
 
 // SharedOptions=--enable-null-aware-operators
 
 import "package:expect/expect.dart";
 import "conditional_access_helper.dart" as h;
@@ skipping 35 matching lines @@
   // generated in the case of o?.m(...).
   { B b = new C(); Expect.equals(1, b?.f(() => 1)); } /// 07: static type warning
   { int i = 1; Expect.equals(null, nullC()?.f(i)); } /// 08: static type warning
 
   // Consequently, '?.' cannot be used to invoke static methods of classes.
   Expect.throws(() => C?.staticMethod(), noMethod); /// 09: static type warning
   Expect.throws(() => h.C?.staticMethod(), noMethod); /// 10: static type warning
 
   // Nor can it be used to access toplevel functions in libraries imported via
   // prefix.
-  Expect.throws(() => h?.topLevelFunction(), noMethod); /// 11: static type warning
+  h?.topLevelFunction(); /// 11: compile-time error
 
   // However, '?.' can be used to access the toString method on the class Type.
   Expect.equals(C?.toString(), (C).toString()); /// 12: ok
   Expect.equals(h.C?.toString(), (h.C).toString()); /// 13: ok
 }