Coverity: Fix several pass-by-values.

webkit/appcache/view_appcache_internals_job.cc

Index: webkit/appcache/view_appcache_internals_job.cc
diff --git a/webkit/appcache/view_appcache_internals_job.cc b/webkit/appcache/view_appcache_internals_job.cc
index da6ff636f93810c2af1db843915768754d9ff2e5..94ee6015f2d65f28d92a30161bd27a68c99aaaca 100644
--- a/webkit/appcache/view_appcache_internals_job.cc
+++ b/webkit/appcache/view_appcache_internals_job.cc
@@ -276,7 +276,7 @@ void EmitHexDump(const char *buf, size_t buf_len, size_t total_len,
   out->append("</pre>");
 }
 
-GURL DecodeBase64URL(const std::string base64) {
+GURL DecodeBase64URL(const std::string& base64) {
   std::string url;
   base::Base64Decode(base64, &url);
   return GURL(url);