Coverity: Fix a pass-by-value.

chrome/browser/visitedlink/visitedlink_master.cc

Index: chrome/browser/visitedlink/visitedlink_master.cc
diff --git a/chrome/browser/visitedlink/visitedlink_master.cc b/chrome/browser/visitedlink/visitedlink_master.cc
index ead98ff0f723d686eff2abbc3fe52bb34918aa14..1c3f0279e12e6e0e72417c6a85ff5e26efab5b47 100644
--- a/chrome/browser/visitedlink/visitedlink_master.cc
+++ b/chrome/browser/visitedlink/visitedlink_master.cc
@@ -65,7 +65,7 @@ void GenerateSalt(uint8 salt[LINK_SALT_LENGTH]) {
 }
 
 // Opens file on a background thread to not block UI thread.
-void AsyncOpen(FILE** file, FilePath filename) {
+void AsyncOpen(FILE** file, const FilePath& filename) {
   *file = OpenFile(filename, "wb+");
   DLOG_IF(ERROR, !(*file)) << "Failed to open file " << filename.value();
 }