Re-apply https://codereview.chromium.org/14636002/, but this time avoid creating TypeMask with dyna…

sdk/lib/_internal/compiler/implementation/types/concrete_types_inferrer.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.
 
 part of types;
 
 class CancelTypeInferenceException {
   final Node node;
   final String reason;
 
@@ skipping 815 matching lines @@
     if (baseType.isUnknown()) {
       return null;
     } else if (baseType.isNull()) {
       return new TypeMask.empty();
     } else {
       ClassBaseType classBaseType = baseType;
       final element = classBaseType.element;
       if (element != null) {
         if (element == compiler.numClass) {
           return new TypeMask.nonNullSubclass(compiler.numClass.rawType);
+        } else if (element == compiler.dynamicClass) {
+          return new TypeMask.nonNullSubclass(compiler.objectClass.rawType);
         } else {
           return new TypeMask.nonNullExact(element.rawType);
         }
       } else {
         return null;
       }
     }
   }
 
   /**
@@ skipping 1211 matching lines @@
   }
 
   void internalError(String reason, {Node node}) {
     inferrer.fail(node, reason);
   }
 
   ConcreteType visitTypeReferenceSend(Send) {
     return inferrer.singletonConcreteType(inferrer.baseTypes.typeBaseType);
   }
 }