Fix some possible performance issues found by clang-tidy

No obvious time differences when building AOSP, but these all seem like
reasonable changes.

1 files changed, 1 insertions, 1 deletions

diff --git a/strutil.cc b/strutil.cc
index 1b99dff..b094198 100644
--- a/strutil.cc
+++ b/strutil.cc
@@ -500,7 +500,7 @@ string ConcatDir(StringPiece b, StringPiece n) {
   return r;
 }
 
-string EchoEscape(const string str) {
+string EchoEscape(const string &str) {
   const char *in = str.c_str();
   string buf;
   for (; *in; in++) {