Avoid a string copy for every CommandLine::HasSwitch query

base/command_line.cc

 // Copyright (c) 2012 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 "base/command_line.h"
 
 #include <algorithm>
 #include <ostream>
 
 #include "base/basictypes.h"
@@ skipping 76 matching lines @@
 #elif defined(OS_POSIX)
       command_line->AppendSwitchNative(switch_string, switch_value);
 #endif
     } else {
       command_line->AppendArgNative(arg);
     }
   }
 }
 
 // Lowercase switches for backwards compatiblity *on Windows*.
+#if defined(OS_WIN)
 std::string LowerASCIIOnWindows(const std::string& string) {
-#if defined(OS_WIN)
   return StringToLowerASCII(string);
+}
 #elif defined(OS_POSIX)
+const std::string& LowerASCIIOnWindows(const std::string& string) {
   return string;
+}
 #endif
-}
 
 
 #if defined(OS_WIN)
 // Quote a string as necessary for CommandLineToArgvW compatiblity *on Windows*.
 string16 QuoteForCommandLineToArgvW(const string16& arg,
                                     bool quote_placeholders) {
   // We follow the quoting rules of CommandLineToArgvW.
   // http://msdn.microsoft.com/en-us/library/17w5ykft.aspx
   string16 quotable_chars(L" \\\"");
   // We may also be required to quote '%', which is commonly used in a command
@@ skipping 326 matching lines @@
 #if defined(OS_WIN)
       arg = QuoteForCommandLineToArgvW(arg, quote_placeholders);
 #endif
       params.append(arg);
     }
   }
   return params;
 }
 
 }  // namespace base