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 339 matching lines @@
 
     void UpdateChecksum();
 
     ScopedFD file_;
     unsigned int file_memory_checksum_;
   };
 #endif
 
   // Creates or opens the given file. Only called if |path_| has no
   // traversal ('..') components.
-  void DoInitialize(uint32 flags);
+  void DoInitialize(uint32 flags, const FilePath& path);

[rvargas (doing something else), 2015/07/02 02:11:05]

tiny nit: Do you mind going back to having path as the first argument?. I also
don't follow why are we documenting on the header that a private member is not
called when the path used is invalid. Granted, that is not part of this CL.

[Dan Beam, 2015/07/02 02:18:06]

Done.

 
   // 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_;
+  // Path that |Initialize()| was called with. Only set if safe (i.e. no '..')

[rvargas (doing something else), 2015/07/02 02:11:06]

I think the safe reference is stale at this point, no?. If the path is not safe,
Initialization will fail and IsValid() will return false, which means the object
is not usable at that point (do we really want to document something about a
member that is only used for tracing, with objects on that state?)

[Dan Beam, 2015/07/02 02:18:06]

Done.

+  // and if file tracing is enabled when |Initialize()| is called.
+  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_