Introduce //components/user_prefs, use to eliminate c/b/prefs dependency in Autofill.

chrome/browser/profiles/profile_impl.cc

Index: chrome/browser/profiles/profile_impl.cc
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 8026e1238352c86c96242fcb7f092b07232285ec..128197db8db8c7b47a53f5ba27c0ac0145a0aaf9 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -55,7 +55,6 @@
 #include "chrome/browser/plugins/plugin_prefs.h"
 #include "chrome/browser/prefs/browser_prefs.h"
 #include "chrome/browser/prefs/chrome_pref_service_factory.h"
-#include "chrome/browser/prefs/pref_registry_syncable.h"
 #include "chrome/browser/prefs/pref_service_syncable.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/prerender/prerender_manager_factory.h"
@@ -81,6 +80,8 @@
 #include "chrome/common/pref_names.h"
 #include "chrome/common/startup_metric_utils.h"
 #include "chrome/common/url_constants.h"
+#include "components/user_prefs/pref_registry_syncable.h"
+#include "components/user_prefs/user_prefs.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/dom_storage_context.h"
 #include "content/public/browser/host_zoom_map.h"
@@ -406,6 +407,8 @@ ProfileImpl::ProfileImpl(
             ExtensionPrefValueMapFactory::GetForProfile(this), false),
         pref_registry_,
         async_prefs));
+    // Register on BrowserContext.
+    components::UserPrefs::Set(this, prefs_.get());
   }
 
   startup_metric_utils::ScopedSlowStartupUMA