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

runtime/bin/builtin.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 <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 // Implementation of native functions which are used for some
 // test/debug functionality in standalone dart mode.
 
 void PrintString(FILE* out, Dart_Handle str) {
   const char* cstring = NULL;
   Dart_Handle result = Dart_StringToCString(str, &cstring);
-  if (!Dart_IsValid(result)) {
+  if (Dart_IsError(result)) {
       cstring = Dart_GetError(result);
   }
   fprintf(out, "%s\n", cstring);
   fflush(out);
 }
 
 
 void FUNCTION_NAME(Logger_PrintString)(Dart_NativeArguments args) {
   Dart_EnterScope();
   PrintString(stdout, Dart_GetNativeArgument(args, 0));
   Dart_ExitScope();
 }
 
 void FUNCTION_NAME(Exit)(Dart_NativeArguments args) {
   Dart_EnterScope();
   int64_t status = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 0));
   Dart_ExitScope();
   exit(status);
 }