Revert of Move JoinString to the base namespace

extensions/common/csp_validator.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/common/csp_validator.h"
 
 #include <vector>
 
 #include "base/strings/string_split.h"
 #include "base/strings/string_tokenizer.h"
@@ skipping 279 matching lines @@
             manifest_errors::kInvalidCSPMissingSecureSrc, kScriptSrc)));
     }
     if (!object_src_status.seen_in_policy && !allow_insecure_object_src) {
       sane_csp_parts.push_back(kObjectSrcDefaultDirective);
       if (warnings)
         warnings->push_back(CSPInstallWarning(ErrorUtils::FormatErrorMessage(
             manifest_errors::kInvalidCSPMissingSecureSrc, kObjectSrc)));
     }
   }
 
-  return base::JoinString(sane_csp_parts, " ");
+  return JoinString(sane_csp_parts, ' ');
 }
 
 bool ContentSecurityPolicyIsSandboxed(
     const std::string& policy, Manifest::Type type) {
   // See http://www.w3.org/TR/CSP/#parse-a-csp-policy for parsing algorithm.
   std::vector<std::string> directives;
   base::SplitString(policy, ';', &directives);
 
   bool seen_sandbox = false;
 
@@ skipping 26 matching lines @@
       }
     }
   }
 
   return seen_sandbox;
 }
 
 }  // namespace csp_validator
 
 }  // namespace extensions