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..0468dd994f62798c577e840a2712d514f1ed447f 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);
 }
@@ -47,12 +47,12 @@ 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(
-           query, "&", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL)) {
+  for (auto param : base::SplitStringPiece(query, "&", base::TRIM_WHITESPACE,

[Nico, 2017/03/15 13:52:11]

const auto&

(imho, s/auto/base::StringPiece/ is even nicer)

[Matt Giuca, 2017/03/17 00:16:27]

See discussion on
https://codereview.chromium.org/2695883003/diff/270001/base/feature_list.cc#n...
--- I think the StringPiece documentation is asking to be used by value, not by
const reference.

(If we want to change it, I'll have to do it globally throughout this CL because
I used this pattern a lot.)

I don't feel strongly about auto vs StringPiece (and it seems the style guide
doesn't either) so I'll revert it.

[Matt Giuca, 2017/03/27 03:24:58]

Done.

+                                           base::SPLIT_WANT_ALL)) {
     if (!HasSameParameterKey(param, safe_parameter) &&
         !HasSameParameterKey(param, ssui_parameter)) {
       new_parameters.push_back(param);