Use Object::null_instance and Object::null_function and do not create Handles everytime.

runtime/vm/dart_api_impl.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 "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/class_finalizer.h"
@@ skipping 5168 matching lines @@
     lib.SetLoadInProgress();
   }
   ASSERT(isolate != NULL);
   const Error& error = Error::Handle(isolate, Compiler::Compile(lib, script));
   if (error.IsNull()) {
     *result = Api::NewHandle(isolate, lib.raw());
   } else {
     *result = Api::NewHandle(isolate, error.raw());
     // Compilation errors are not Dart instances, so just mark the library
     // as having failed to load without providing an error instance.
-    lib.SetLoadError(Instance::Handle());
+    lib.SetLoadError(Object::null_instance());
   }
 }
 
 
 DART_EXPORT Dart_Handle Dart_LoadScript(Dart_Handle url,
                                         Dart_Handle source,
                                         intptr_t line_offset,
                                         intptr_t column_offset) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
@@ skipping 817 matching lines @@
   ASSERT(stream != NULL);
   TimelineEvent* event = stream->StartEvent();
   if (event != NULL) {
     event->AsyncEnd(label, async_id);
     event->Complete();
   }
   return Api::Success();
 }
 
 }  // namespace dart