Revert of Delete base/prefs and update callers to use components.

components/prefs/pref_service_factory.cc

Index: components/prefs/pref_service_factory.cc
diff --git a/components/prefs/pref_service_factory.cc b/components/prefs/pref_service_factory.cc
index 663695da98895e0b18f7bd4297fc261e71bff5eb..e8b9bb448786ee7c456cd454c1dec3966651003c 100644
--- a/components/prefs/pref_service_factory.cc
+++ b/components/prefs/pref_service_factory.cc
@@ -12,6 +12,8 @@
 #include "components/prefs/pref_notifier_impl.h"
 #include "components/prefs/pref_service.h"
 #include "components/prefs/pref_value_store.h"
+
+namespace base {
 
 namespace {
 
@@ -59,3 +61,5 @@
                       async_));
   return pref_service;
 }
+
+}  // namespace base