Move PrefStoreManagerImpl into //services/preferences.

services/preferences/BUILD.gn

Index: services/preferences/BUILD.gn
diff --git a/services/preferences/BUILD.gn b/services/preferences/BUILD.gn
index 524b6bd8a28ed2f6b959f0688e8bc833f017b029..cbc994af3c98d474863e44d038fbfee7ab68297d 100644
--- a/services/preferences/BUILD.gn
+++ b/services/preferences/BUILD.gn
@@ -18,17 +18,22 @@ service_manifest("manifest") {
 }
 
 source_set("preferences") {
-  public_deps = [
-    "//services/preferences/public/interfaces",
+  visibility = [
+    ":*",
+    "//services/preferences/public/cpp:service_main",
   ]
   deps = [
     "//components/prefs",
+    "//services/preferences/public/interfaces",
+    "//services/service_manager/public/cpp",
   ]
   sources = [
     "persistent_pref_store_factory.cc",
     "persistent_pref_store_factory.h",
     "persistent_pref_store_impl.cc",
     "persistent_pref_store_impl.h",
+    "pref_store_manager_impl.cc",
+    "pref_store_manager_impl.h",
   ]
 }