Fix test failure issue 7471: Signature classes have different type checking rules, i.e., they have …

runtime/vm/flow_graph_compiler.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 "vm/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
@@ skipping 1002 matching lines @@
 }
 
 
 // Returns true if checking against this type is a direct class id comparison.
 bool FlowGraphCompiler::TypeCheckAsClassEquality(const AbstractType& type) {
   ASSERT(type.IsFinalized() && !type.IsMalformed());
   // Requires CHA, which can be applied in optimized code only,
   if (!FLAG_use_cha || !is_optimizing()) return false;
   if (!type.IsInstantiated()) return false;
   const Class& type_class = Class::Handle(type.type_class());
+  // Signature classes have different type checking rules.
+  if (type_class.IsSignatureClass()) return false;
   // Could be an interface check?
   if (type_class.is_implemented()) return false;
   const intptr_t type_cid = type_class.id();
   if (CHA::HasSubclasses(type_cid)) return false;
   if (type_class.HasTypeArguments()) {
     // Only raw types can be directly compared, thus disregarding type
     // arguments.
     const AbstractTypeArguments& type_arguments =
         AbstractTypeArguments::Handle(type.arguments());
     const bool is_raw_type = type_arguments.IsNull() ||
         type_arguments.IsRaw(type_arguments.Length());
     return is_raw_type;
   }
   return true;
 }
 
 }  // namespace dart