Destroy the UserManager after ChromeBrowserMainPartsLinux::PostMainMessageLoopRun

UserManager is needed during MergeSessionThrottle::ShouldShowMergeSessionPage, which appears sometimes to be triggered during ChromeBrowserMainPartsLinux::PostMainMessageLoopRun.

I observed this during the test TrayAccessibilityTest.ShowMenu, as described in https://crbug.com/243364#c12. However, at most occasions this was masked by ShouldShowMergeSessionPage being actually triggered earlier.

This is restoring the order of destroying UserManager and calling ChromeBrowserMainPartsLinux::PostMainMessageLoopRun to the state before the CL https://chromiumcodereview.appspot.com/15702004/.

BUG=243364

Review URL: https://chromiumcodereview.appspot.com/15769004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202617 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

@@ -849,10 +849,13 @@ void ChromeBrowserMainPartsChromeos::PostMainMessageLoopRun() {
 
   chrome::CloseAsh();
 
-  // Destroy the UserManager after ash has been destroyed.
-  UserManager::Destroy();
-
   ChromeBrowserMainPartsLinux::PostMainMessageLoopRun();
+
+  // Destroy the UserManager after ash has been destroyed and
+  // ChromeBrowserMainPartsLinux::PostMainMessageLoopRun run.  The latter might
+  // trigger MergeSessionThrottle::ShouldShowMergeSessionPage, which requires
+  // the UserManager to exist.
+  UserManager::Destroy();
 }
 
 void ChromeBrowserMainPartsChromeos::PostDestroyThreads() {