update engine: 32- and 64-bit compile

Review URL: http://codereview.chromium.org/1599029
diff --git a/utils.cc b/utils.cc
index e1ed874..ff3c9db 100644
--- a/utils.cc
+++ b/utils.cc
@@ -80,7 +80,7 @@
       reinterpret_cast<const unsigned char* const>(arr);
   LOG(INFO) << "Logging array of length: " << length;
   const unsigned int bytes_per_line = 16;
-  for (size_t i = 0; i < length; i += bytes_per_line) {
+  for (uint32_t i = 0; i < length; i += bytes_per_line) {
     const unsigned int bytes_remaining = length - i;
     const unsigned int bytes_per_this_line = min(bytes_per_line,
                                                  bytes_remaining);