Change namespace chromeos => ash for //c/b/ash/settings

Code in //chrome/browser/ash/settings is a part of the ash-chrome, so
namespace is changed to ash from chromeos.

To avoid churn during other namespace transitions in future, this CL has
temporary 'using' declarations.

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

Bug: 1164001
Change-Id: I6a1cf768b81534c61a223ad7b0e5c5854d867573
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2727220
Reviewed-by: Hidehiko Abe <[email protected]>
Owners-Override: Hidehiko Abe <[email protected]>
Commit-Queue: Yeunjoo Choi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#861876}
diff --git a/chrome/browser/ui/webui/help/help_utils_chromeos.cc b/chrome/browser/ui/webui/help/help_utils_chromeos.cc
index cfddc57..b2a4f3ca 100644
--- a/chrome/browser/ui/webui/help/help_utils_chromeos.cc
+++ b/chrome/browser/ui/webui/help/help_utils_chromeos.cc
@@ -23,7 +23,7 @@
       interactive ? true : chromeos::switches::IsCellularFirstDevice();
 
   // Device Policy overrides the defaults.
-  chromeos::CrosSettings* settings = chromeos::CrosSettings::Get();
+  ash::CrosSettings* settings = ash::CrosSettings::Get();
   if (!settings)
     return default_update_over_cellular_allowed;