Fix DART_CHECK_VALID macro.

runtime/include/dart_api.h

 // 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.
 
 #ifndef INCLUDE_DART_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
  *
  * Dart is a class-based programming language for creating structured
@@ skipping 309 matching lines @@
                                          const char* handle_string,
                                          const char* error);
 
 // TODO(turnidge): Move DART_CHECK_VALID to some sort of dart_utils
 // header instead of this header.
 /**
  * Aborts the process if 'handle' is an error handle.
  *
  * Provided for convenience.
  */
-#define DART_CHECK_VALID(handle)                                        \
-  if (Dart_IsError((handle))) {                                         \
-    _Dart_ReportErrorHandle(__FILE__, __LINE__,                       \
-                              #handle, Dart_GetError(handle));          \
-  }
+#define DART_CHECK_VALID(handle)                                               \
+  {                                                                            \
+    Dart_Handle __handle = handle;                                             \
+    if (Dart_IsError((__handle))) {                                            \
+      _Dart_ReportErrorHandle(__FILE__, __LINE__,                              \
+                              #handle, Dart_GetError(__handle));               \
+    }                                                                          \
+  }                                                                            \
 
 
 /**
  * Converts an object to a string.
  *
  * May generate an unhandled exception error.
  *
  * \return The converted string if no error occurs during
  *   the conversion. If an error does occur, an error handle is
  *   returned.
@@ skipping 2217 matching lines @@
  *
  * \param object An object.
  * \param peer A value to store in the peer field.
  *
  * \return Returns an error if 'object' is a subtype of Null, num, or
  *   bool.
  */
 DART_EXPORT Dart_Handle Dart_SetPeer(Dart_Handle object, void* peer);
 
 #endif  // INCLUDE_DART_API_H_