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

base/platform_file.cc

Index: base/platform_file.cc
===================================================================
--- base/platform_file.cc	(revision 175576)
+++ base/platform_file.cc	(working copy)
@@ -14,4 +14,15 @@
 
 PlatformFileInfo::~PlatformFileInfo() {}
 
+PlatformFile CreatePlatformFile(const FilePath& name,
+                                int flags,
+                                bool* created,
+                                PlatformFileError* error) {
+  if (name.ReferencesParent()) {
+    *error = PLATFORM_FILE_ERROR_ACCESS_DENIED;
+    return kInvalidPlatformFileValue;
+  }
+  return CreatePlatformFileUnsafe(name, flags, created, error);
+}
+
 }  // namespace base