Change uses of base::JoinString to pass StringPieces where possible.

chrome/browser/net/safe_search_util.cc

Index: chrome/browser/net/safe_search_util.cc
diff --git a/chrome/browser/net/safe_search_util.cc b/chrome/browser/net/safe_search_util.cc
index cc1f6ded87a0c8f23fcc05bdcfb8298fe889a988..ba59b774e3a76fbdda873c94d3da106586b89dca 100644
--- a/chrome/browser/net/safe_search_util.cc
+++ b/chrome/browser/net/safe_search_util.cc
@@ -33,12 +33,12 @@ const char kYouTubeRestrictHeaderValueStrict[] = "Strict";
 // Returns whether a URL parameter, |first_parameter| (e.g. foo=bar), has the
 // same key as the the |second_parameter| (e.g. foo=baz). Both parameters
 // must be in key=value form.
-bool HasSameParameterKey(const std::string& first_parameter,
-                         const std::string& second_parameter) {
+bool HasSameParameterKey(base::StringPiece first_parameter,
+                         base::StringPiece second_parameter) {
   DCHECK(second_parameter.find("=") != std::string::npos);
   // Prefix for "foo=bar" is "foo=".
-  std::string parameter_prefix = second_parameter.substr(
-      0, second_parameter.find("=") + 1);
+  base::StringPiece parameter_prefix =
+      second_parameter.substr(0, second_parameter.find("=") + 1);
   return base::StartsWith(first_parameter, parameter_prefix,
                           base::CompareCase::INSENSITIVE_ASCII);
 }
@@ -47,11 +47,11 @@ bool HasSameParameterKey(const std::string& first_parameter,
 // so that SafeSearch is active. |query| is the string to examine and the
 // return value is the |query| string modified such that SafeSearch is active.
 std::string AddSafeSearchParameters(const std::string& query) {
-  std::vector<std::string> new_parameters;
+  std::vector<base::StringPiece> new_parameters;
   std::string safe_parameter = chrome::kSafeSearchSafeParameter;
   std::string ssui_parameter = chrome::kSafeSearchSsuiParameter;
 
-  for (const std::string& param : base::SplitString(
+  for (const base::StringPiece& param : base::SplitStringPiece(
            query, "&", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL)) {
     if (!HasSameParameterKey(param, safe_parameter) &&
         !HasSameParameterKey(param, ssui_parameter)) {