Only set File::[tracing_]path_ when file tracing is enabled.

base/files/file.h

 // 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.
 
 #ifndef BASE_FILES_FILE_H_
 #define BASE_FILES_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 337 matching lines @@
     // failing a CHECK if they do not.
     void Check() const;
 
     void UpdateChecksum();
 
     ScopedFD file_;
     unsigned int file_memory_checksum_;
   };
 #endif
 
-  // Creates or opens the given file. Only called if |path_| has no
+  // Creates or opens the given file. Only called if |path| has no
   // traversal ('..') components.
-  void DoInitialize(uint32 flags);
+  void DoInitialize(const FilePath& path, uint32 flags);
 
   // TODO(tnagel): Reintegrate into Flush() once histogram isn't needed anymore,
   // cf. issue 473337.
   bool DoFlush();
 
   void SetPlatformFile(PlatformFile file);
 
 #if defined(OS_WIN)
   win::ScopedHandle file_;
 #elif defined(OS_POSIX)
   MemoryCheckingScopedFD file_;
 #endif
 
-  // Path that |Initialize()| was called with. Only set if safe (i.e. no '..').
-  FilePath path_;
+  // A path to use for tracing purposes. Set if file tracing is enabled during
+  // |Initialize()|.
+  FilePath tracing_path_;
 
   // Object tied to the lifetime of |this| that enables/disables tracing.
   FileTracing::ScopedEnabler trace_enabler_;
 
   Error error_details_;
   bool created_;
   bool async_;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_H_