Convert prefix search in UserScript code to use base::StartsWith()

extensions/browser/web_ui_user_script_loader.cc

 // Copyright 2015 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/browser/web_ui_user_script_loader.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
@@ skipping 110 matching lines @@
       fetchers_.push_back(std::move(fetcher));
     }
   }
 }
 
 void WebUIUserScriptLoader::OnSingleWebUIURLFetchComplete(
     extensions::UserScript::File* script_file,
     bool success,
     const std::string& data) {
   if (success) {
-    // Remove BOM from the content.
-    std::string::size_type index = data.find(base::kUtf8ByteOrderMark);
-    if (index == 0)
+    // Remove BOM from |data|.
+    if (base::StartsWith(data, base::kUtf8ByteOrderMark,
+                         base::CompareCase::SENSITIVE)) {
       script_file->set_content(data.substr(strlen(base::kUtf8ByteOrderMark)));
-    else
+    } else {
       script_file->set_content(data);
+    }
   }
 
   ++complete_fetchers_;
   if (complete_fetchers_ == fetchers_.size()) {
     complete_fetchers_ = 0;
     OnWebUIURLFetchComplete();
     fetchers_.clear();
   }
 }
 
 void WebUIUserScriptLoader::OnWebUIURLFetchComplete() {
   content::BrowserThread::PostTask(
       content::BrowserThread::FILE, FROM_HERE,
       base::Bind(&SerializeOnFileThread, base::Passed(&user_scripts_cache_),
                  scripts_loaded_callback_));
   scripts_loaded_callback_.Reset();
 }