linux and chromeos: Turn on -Wunused-const-variable.

chrome/browser/extensions/api/usb/usb_api.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 "chrome/browser/extensions/api/usb/usb_api.h"
 
 #include <string>
 #include <vector>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 47 matching lines @@
 
 const char kDataKey[] = "data";
 const char kResultCodeKey[] = "resultCode";
 
 const char kErrorInitService[] = "Failed to initialize USB service.";
 
 const char kErrorOpen[] = "Failed to open device.";
 const char kErrorCancelled[] = "Transfer was cancelled.";
 const char kErrorDisconnect[] = "Device disconnected.";
 const char kErrorGeneric[] = "Transfer failed.";
+#if !defined(OS_CHROMEOS)
 const char kErrorNotSupported[] = "Not supported on this platform.";
+#endif
 const char kErrorOverflow[] = "Inbound transfer overflow.";
 const char kErrorStalled[] = "Transfer stalled.";
 const char kErrorTimeout[] = "Transfer timed out.";
 const char kErrorTransferLength[] = "Transfer length is insufficient.";
 
 const char kErrorCannotListInterfaces[] = "Error listing interfaces.";
 const char kErrorCannotClaimInterface[] = "Error claiming interface.";
 const char kErrorCannotReleaseInterface[] = "Error releasing interface.";
 const char kErrorCannotSetInterfaceAlternateSetting[] =
     "Error setting alternate interface setting.";
@@ skipping 1083 matching lines @@
     SetResult(new base::FundamentalValue(false));
     CompleteWithError(kErrorResetDevice);
     return;
   }
 
   SetResult(new base::FundamentalValue(true));
   AsyncWorkCompleted();
 }
 
 }  // namespace extensions