Don't allow path traversal paths on the base file helpers

base/platform_file_posix.cc

Index: base/platform_file_posix.cc
===================================================================
--- base/platform_file_posix.cc	(revision 175095)
+++ base/platform_file_posix.cc	(working copy)
@@ -41,8 +41,10 @@
 #endif
 
 // TODO(erikkay): does it make sense to support PLATFORM_FILE_EXCLUSIVE_* here?
-PlatformFile CreatePlatformFile(const FilePath& name, int flags,
-                                bool* created, PlatformFileError* error_code) {
+PlatformFile CreatePlatformFileAllowTraversal(const FilePath& name,
+                                              int flags,
+                                              bool* created,
+                                              PlatformFileError* error_code) {
   base::ThreadRestrictions::AssertIOAllowed();
 
   int open_flags = 0;