Add utility method for WebString to base::FilePath conversion

third_party/WebKit/public/platform/FilePathConversion.h

 // Copyright 2016 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.
 
-#ifndef URLConversion_h
-#define URLConversion_h
+#ifndef FilePathConversion_h
+#define FilePathConversion_h
 
 #include "WebCommon.h"
 
-class GURL;
+namespace base {
+class FilePath;
+}
 
 namespace blink {
 
 class WebString;
 
-BLINK_COMMON_EXPORT GURL WebStringToGURL(const WebString&);
+BLINK_COMMON_EXPORT base::FilePath WebStringToFilePath(const WebString&);
 
 } // namespace blink
 
-#endif
+#endif // FilePathConversion_h