mojo: Fix mojo test on Art runtime.

mojo/android/javatests/validation_test_util.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/android/javatests/validation_test_util.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/test/test_support_android.h"
@@ skipping 13 matching lines @@
   std::vector<uint8_t> data;
   size_t num_handles;
   std::string error_message;
   if (!test::ParseValidationTestInput(
           input, &data, &num_handles, &error_message)) {
     ScopedJavaLocalRef<jstring> j_error_message =
         base::android::ConvertUTF8ToJavaString(env, error_message);
     return Java_ValidationTestUtil_buildData(
                env, NULL, 0, j_error_message.obj()).Release();
   }
-
+  void* data_ptr = &data[0];
+  if (!data_ptr) {
+    DCHECK(!data.size());
+    data_ptr = &data;
+  }
   jobject byte_buffer =
-      env->NewDirectByteBuffer(&data[0], data.size());
+      env->NewDirectByteBuffer(data_ptr, data.size());
   return Java_ValidationTestUtil_buildData(env, byte_buffer, num_handles, NULL)
       .Release();
 }
 
 }  // namespace android
 }  // namespace mojo