Fix crash with --trace-deoptimization-verbose and tweak formatting.

runtime/vm/deferred_objects.cc

 // Copyright (c) 2013, 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/deferred_objects.h"
 
 #include "vm/deopt_instructions.h"
 #include "vm/flags.h"
 #include "vm/object.h"
 
@@ skipping 70 matching lines @@
     OS::PrintErr("materializing Int32x4 at %" Px ": %x,%x,%x,%x\n",
                  reinterpret_cast<uword>(slot()), x, y, z, w);
   }
 }
 
 
 void DeferredObjectRef::Materialize(DeoptContext* deopt_context) {
   DeferredObject* obj = deopt_context->GetDeferredObject(index());
   *slot() = obj->object();
   if (FLAG_trace_deoptimization_verbose) {
-    OS::PrintErr("writing instance ref at %" Px ": %s\n",
-                 reinterpret_cast<uword>(slot()),
-                 Instance::Handle(obj->object()).ToCString());
+    const Class& cls = Class::Handle(Isolate::Current()->class_table()->At(
+        Object::Handle(obj->object()).GetClassId()));
+    OS::PrintErr("writing instance of class %s ref at %" Px ".\n",
+                 cls.ToCString(),
+                 reinterpret_cast<uword>(slot()));
   }
 }
 
 
 RawInstance* DeferredObject::object() {
   if (object_ == NULL) {
     Create();
   }
   return object_->raw();
 }
@@ skipping 49 matching lines @@
       if (FLAG_trace_deoptimization_verbose) {
         OS::PrintErr("    null Field @ offset(%" Pd ") <- %s\n",
                      offset.Value(),
                      value.ToCString());
       }
     }
   }
 }
 
 }  // namespace dart