Deal with unhandled exceptions the same way in all Dart api functions.

runtime/bin/eventhandler.cc

 // Copyright (c) 2011, 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 "bin/dartutils.h"
 #include "bin/eventhandler.h"
 
 #include "include/dart_api.h"
 
 
 static const intptr_t kNativeEventHandlerFieldIndex = 0;
 
 
 /*
  * Returns the reference of the EventHandler stored in the native field.
  */
 static EventHandler* GetEventHandler(Dart_Handle handle) {
   intptr_t value = 0;
   Dart_Handle result = Dart_GetNativeInstanceField(
       handle, kNativeEventHandlerFieldIndex, &value);
-  ASSERT(Dart_IsValid(result));
+  ASSERT(!Dart_IsError(result));
   EventHandler* event_handler = reinterpret_cast<EventHandler*>(value);
   ASSERT(event_handler != NULL);
   return event_handler;
 }
 
 
 /*
  * Sets the reference of the EventHandler in the native field.
  */
 static void SetEventHandler(Dart_Handle handle, EventHandler* event_handler) {
@@ skipping 27 matching lines @@
   Dart_Handle handle = Dart_GetNativeArgument(args, 0);
   EventHandler* event_handler = GetEventHandler(handle);
   intptr_t id = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 1));
   handle = Dart_GetNativeArgument(args, 2);
   Dart_Port dart_port =
       DartUtils::GetIntegerInstanceField(handle, DartUtils::kIdFieldName);
   intptr_t data = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 3));
   event_handler->SendData(id, dart_port, data);
   Dart_ExitScope();
 }