Control zero suggest with a pref, not a switch.

chrome/browser/prefs/browser_prefs.cc

Index: chrome/browser/prefs/browser_prefs.cc
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 8a063b1cf14e49fc265e0be44fec23c172716ded..c03af7d12cab21e9d1c5d257a9bd944c409fd3fe 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -6,6 +6,7 @@
 
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/accessibility/invert_bubble_prefs.h"
+#include "chrome/browser/autocomplete/zero_suggest_provider.h"
 #include "chrome/browser/autofill/autofill_manager.h"
 #include "chrome/browser/background/background_mode_manager.h"
 #include "chrome/browser/bookmarks/bookmark_utils.h"
@@ -223,6 +224,7 @@ void RegisterUserPrefs(PrefService* user_prefs) {
   TemplateURLPrepopulateData::RegisterUserPrefs(user_prefs);
   TranslatePrefs::RegisterUserPrefs(user_prefs);
   web_intents::RegisterUserPrefs(user_prefs);
+  ZeroSuggestProvider::RegisterUserPrefs(user_prefs);
 
 #if defined(ENABLE_CONFIGURATION_POLICY)
   policy::URLBlacklistManager::RegisterPrefs(user_prefs);