strnlen is not always available.

runtime/vm/snapshot.cc

 // 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.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 722 matching lines @@
     return ApiError::New(msg, Heap::kOld);
   }
   Advance(version_len);
 
   const char* expected_features = Dart::FeaturesString(kind_);
   ASSERT(expected_features != NULL);
   const intptr_t expected_len = strlen(expected_features);
 
   const char* features = reinterpret_cast<const char*>(CurrentBufferAddress());
   ASSERT(features != NULL);
-  intptr_t buffer_len = strnlen(features, PendingBytes());
+  intptr_t buffer_len = OS::StrNLen(features, PendingBytes());
   if ((buffer_len != expected_len) ||
       strncmp(features, expected_features, expected_len)) {
     const intptr_t kMessageBufferSize = 256;
     char message_buffer[kMessageBufferSize];
     char* actual_features = OS::StrNDup(features, buffer_len < 128 ? buffer_len
                                                                    : 128);
     OS::SNPrint(message_buffer,
                 kMessageBufferSize,
                 "Wrong features in snapshot, expected '%s' found '%s'",
                 expected_features,
@@ skipping 2076 matching lines @@
   if (setjmp(*jump.Set()) == 0) {
     NoSafepointScope no_safepoint;
     WriteObject(obj.raw());
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart