Cleanup: Pass std::string as const reference from chrome/

Passing std::string by reference can prevent extra copying of object.

BUG=367418
TEST=
[email protected],[email protected],[email protected]

Review URL: https://codereview.chromium.org/1358783002

Cr-Commit-Position: refs/heads/master@{#351009}
diff --git a/chrome/browser/net/sdch_browsertest.cc b/chrome/browser/net/sdch_browsertest.cc
index 9c93d6b..406aeca 100644
--- a/chrome/browser/net/sdch_browsertest.cc
+++ b/chrome/browser/net/sdch_browsertest.cc
@@ -131,9 +131,8 @@
 class SdchResponseHandler {
  public:
   // Do initial preparation so that SDCH requests can be handled.
-  explicit SdchResponseHandler(std::string domain)
-      : cache_sdch_response_(false),
-        weak_ptr_factory_(this) {
+  explicit SdchResponseHandler(const std::string& domain)
+      : cache_sdch_response_(false), weak_ptr_factory_(this) {
     // Dictionary
     sdch_dictionary_contents_ = "Domain: ";
     sdch_dictionary_contents_ += domain;