Revert of Move JoinString to the base namespace

chrome/browser/net/predictor.cc

Index: chrome/browser/net/predictor.cc
diff --git a/chrome/browser/net/predictor.cc b/chrome/browser/net/predictor.cc
index 0241aa0d39cdfdbf457a440cd3ff8243d68d6de5..9299b63358dec01e1bdd97292cf68ec474d075b8 100644
--- a/chrome/browser/net/predictor.cc
+++ b/chrome/browser/net/predictor.cc
@@ -504,7 +504,7 @@
     std::vector<std::string> parts;
     base::SplitString(url.host(), '.', &parts);
     std::reverse(parts.begin(), parts.end());
-    std::string reversed_host = base::JoinString(parts, ".");
+    std::string reversed_host = JoinString(parts, '.');
 
     // Return the new URL.
     GURL::Replacements url_components;