Fix some warnings.

lib/compiler/implementation/js_backend/backend.dart

 // 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.
 
 typedef void Recompile(Element element);
 
 class ReturnInfo {
   HType returnType;
   List<Element> compiledFunctions;
 
@@ skipping 907 matching lines @@
         return nativeCheck
             ? const SourceString('listSuperNativeTypeCheck')
             : const SourceString('listSuperTypeCheck');
       } else {
         return nativeCheck
             ? const SourceString('callTypeCheck')
             : const SourceString('propertyTypeCheck');
       }
     }
   }
+
+  void dumpInferredTypes() {
+    print("Inferred argument types:");
+    print("------------------------");
+    argumentTypes.dump();
+    print("");
+    print("Inferred return types:");
+    print("----------------------");
+    dumpReturnTypes();
+    print("");
+    print("Inferred field types:");
+    print("------------------------");
+    fieldTypes.dump();
+    print("");
+  }
 }