Use const auto& in for loops.

Change-Id: Ic437c59797ee4e7dc38291da35c72d827bc89c8d
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 500377c..0a97abc 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -832,11 +832,10 @@
 }
 
 TEST(unistd, sysconf_SC_NPROCESSORS_ONLN) {
-  std::string s;
-  ASSERT_TRUE(android::base::ReadFileToString("/sys/devices/system/cpu/online", &s));
-  std::vector<std::string> strs = android::base::Split(s, ",");
+  std::string line;
+  ASSERT_TRUE(android::base::ReadFileToString("/sys/devices/system/cpu/online", &line));
   long online_cpus = 0;
-  for (auto& s : strs) {
+  for (const std::string& s : android::base::Split(line, ",")) {
     std::vector<std::string> numbers = android::base::Split(s, "-");
     if (numbers.size() == 1u) {
       online_cpus++;