Make EfficientLength extend Iterable.

runtime/vm/debugger_api_impl_test.cc

 // Copyright (c) 2012, 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.
 
 #include "include/dart_mirrors_api.h"
 #include "include/dart_tools_api.h"
 #include "platform/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/lockers.h"
 #include "vm/unit_test.h"
@@ skipping 2239 matching lines @@
   }
   {
     Dart_Handle super_type = Dart_GetSupertype(Test5_int_type);
     const Type& expected_type = Api::UnwrapTypeHandle(zone, Test4_int_type);
     const Type& actual_type = Api::UnwrapTypeHandle(zone, super_type);
     EXPECT(expected_type.raw() == actual_type.raw());
   }
   {
     Dart_Handle set_type = Dart_GetType(core_lib, set_name, 0, NULL);
     Dart_Handle super_type = Dart_GetSupertype(set_type);
+    Dart_Handle super2_type = Dart_GetSupertype(super_type);
     Dart_Handle iterable_type = Dart_GetType(core_lib, iterable_name, 0, NULL);
     const Type& expected_type = Api::UnwrapTypeHandle(zone, iterable_type);
-    const Type& actual_type = Api::UnwrapTypeHandle(zone, super_type);
+    const Type& actual_type = Api::UnwrapTypeHandle(zone, super2_type);
     EXPECT(expected_type.raw() == actual_type.raw());
   }
   {
     Dart_Handle list_type = Dart_GetType(core_lib, list_name, 0, NULL);
     Dart_Handle super_type = Dart_GetSupertype(list_type);
     EXPECT(!Dart_IsError(super_type));
     super_type = Dart_GetSupertype(super_type);
     EXPECT(!Dart_IsError(super_type));
     EXPECT(super_type == Dart_Null());
   }
@@ skipping 87 matching lines @@
       " null, 5, 17, 5, 18, 9, 19, 12,"
       " null, 6, 21, 1,"
       " null, 8, 24, 1, 25, 5, 26, 6, 27, 8,"
       " null, 9, 29, 1]",
       tokens_cstr);
 }
 
 #endif
 
 }  // namespace dart