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

base/files/file.h

Index: base/files/file.h
diff --git a/base/files/file.h b/base/files/file.h
index 94ef56fbbc8fae9be21f93a38dbad1e49a06de20..cba435363560187f60341cad8c865ed1d576b291 100644
--- a/base/files/file.h
+++ b/base/files/file.h
@@ -355,9 +355,9 @@ class BASE_EXPORT File {
   };
 #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.
@@ -371,8 +371,9 @@ class BASE_EXPORT File {
   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_;