Add strnlen() wrapper and its test

util/stdlib/strnlen.cc

Index: util/stdlib/strnlen.cc
diff --git a/util/stdlib/strnlen.cc b/util/stdlib/strnlen.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b17796bb8e439152dfd9d37c888bb6ee1cd7554d
--- /dev/null
+++ b/util/stdlib/strnlen.cc
@@ -0,0 +1,37 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/stdlib/strnlen.h"
+
+namespace crashpad {
+
+#if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7
+size_t strnlen(const char* string, size_t max_length) {
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
+  if (::strnlen) {
+    return ::strnlen(string, max_length);
+  }
+#endif
+
+  for (size_t index = 0; index < max_length; ++index) {
+    if (string[index] == '\0') {
+      return index;
+    }
+  }
+
+  return max_length;
+}
+#endif
+
+}  // namespace crashpad