Fix warnings in system/extras.

Bug: http://b/26936282
Change-Id: I1b9c6c9bb06944c32abcb871279d056eea0fb11a
diff --git a/memtrack/memtrack.cpp b/memtrack/memtrack.cpp
index a451d5c..2c4d7c0 100644
--- a/memtrack/memtrack.cpp
+++ b/memtrack/memtrack.cpp
@@ -248,7 +248,7 @@
   for (std::vector<const process_info_t *>::const_iterator it = list_.begin();
        it != list_.end(); ++it) {
     ALOGI("  Name: %s", (*it)->name.c_str());
-    ALOGI("    Max running processes: %d", (*it)->max_num_pids);
+    ALOGI("    Max running processes: %zu", (*it)->max_num_pids);
     if ((*it)->pids.size() > 0) {
       ALOGI("    Currently running pids:");
       for (std::vector<int>::const_iterator pid_it = (*it)->pids.begin();