Move //c/b/ash/account_manager to namespace ash

Read chrome/browser/ash/README.md for the rationale.

To avoid having to make namespace changes twice, code that will be
eventually moved to namespace ash is changed to additionally export its
symbols in the newer namespace.

This CL is part of the Chrome OS source code directory migration:
https://docs.google.com/document/d/1g-98HpzA8XcoGBWUv1gQNr4rbnD5yfvbtYZyPDDbkaE.

Bug: 1164001
Change-Id: Ia413e490af89a53cae945ca839c35f27bfd446fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2656596
Owners-Override: James Cook <[email protected]>
Commit-Queue: Henrique Ferreiro <[email protected]>
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#848337}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 6788f985..353400f 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -1044,7 +1044,7 @@
   chromeos::RegisterSamlProfilePrefs(registry);
   chromeos::ScreenTimeController::RegisterProfilePrefs(registry);
   SecondaryAccountConsentLogger::RegisterPrefs(registry);
-  chromeos::EduCoexistenceConsentInvalidationController::RegisterProfilePrefs(
+  ash::EduCoexistenceConsentInvalidationController::RegisterProfilePrefs(
       registry);
   SigninErrorNotifier::RegisterPrefs(registry);
   chromeos::ServicesCustomizationDocument::RegisterProfilePrefs(registry);