Make PrefService available in *ash

ash/mus/shell_delegate_mus.cc

Index: ash/mus/shell_delegate_mus.cc
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index f0932ce7e5b20185ee9ac052a39283b9c0774a87..4c4f55cd44766adacaac69a2f78c64f6e1b16377 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -155,6 +155,11 @@ gfx::Image ShellDelegateMus::GetDeprecatedAcceleratorImage() const {
   return gfx::Image();
 }
 
+PrefService* ShellDelegateMus::GetActiveUserPrefService() const {
+  NOTREACHED();

[sky, 2017/04/26 19:51:57]

Please add a comment as to why the NOTREACHED as it isn't obvious from looking
at this code why it's here.

[afakhry, 2017/04/26 22:43:50]

Done.

+  return nullptr;
+}
+
 bool ShellDelegateMus::IsTouchscreenEnabledInPrefs(bool use_local_state) const {
   NOTIMPLEMENTED();
   return true;