Document rollback dependency on oobe flag

Document that the path to the oobe-completed flag should be changed in
the file for rollback constants as well if it is changed in Chromium.

Bug: 1124428
Change-Id: Ie817dcb534ef6a326076995923db310f2b170f10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435389Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Miriam Polzer <mpolzer@google.com>
Cr-Commit-Position: refs/heads/master@{#812614}

chrome/browser/chromeos/login/startup_utils.cc

@@ -56,6 +56,8 @@ void SaveStringPreferenceForced(const char* pref_name,
 // On Linux desktop, returns {DIR_USER_DATA}/.oobe_completed.
 base::FilePath GetOobeCompleteFlagPath() {
   // The constant is defined here so it won't be referenced directly.
+  // If you change this path make sure to also change the corresponding rollback
+  // constant in Chrome OS: src/platform2/oobe_config/rollback_constants.cc
   const char kOobeCompleteFlagFilePath[] = "/home/chronos/.oobe_completed";
 
   if (base::SysInfo::IsRunningOnChromeOS()) {