Control zero suggest with a pref, not a switch.

chrome/browser/autocomplete/zero_suggest_provider.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/autocomplete/zero_suggest_provider.h"
 
 #include "base/callback.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/string16.h"
 #include "base/string_util.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/autocomplete/autocomplete_input.h"
 #include "chrome/browser/autocomplete/autocomplete_match.h"
 #include "chrome/browser/autocomplete/autocomplete_provider_listener.h"
+#include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_service.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
+#include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/load_flags.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_fetcher.h"
 #include "net/url_request/url_request_status.h"
 
 namespace {
 // The relevance of the top match from this provider.
 const int kMaxZeroSuggestRelevance = 100;
 }  // namespace
 
+// static
+ZeroSuggestProvider* ZeroSuggestProvider::Create(
+    AutocompleteProviderListener* listener,
+    Profile* profile) {
+  if (profile && !profile->IsOffTheRecord() && profile->GetPrefs()) {
+    std::string url_prefix = profile->GetPrefs()->GetString(
+        prefs::kExperimentalZeroSuggestUrlPrefix);
+    if (!url_prefix.empty())
+      return new ZeroSuggestProvider(listener, profile, url_prefix);
+  }
+  return NULL;
+}
+
 ZeroSuggestProvider::ZeroSuggestProvider(
   AutocompleteProviderListener* listener,
   Profile* profile,
   const std::string& url_prefix)
     : AutocompleteProvider(listener, profile,
           AutocompleteProvider::TYPE_ZERO_SUGGEST),
       url_prefix_(url_prefix),
       template_url_service_(TemplateURLServiceFactory::GetForProfile(profile)) {
 }
 
+// static
+void ZeroSuggestProvider::RegisterUserPrefs(PrefService* user_prefs) {
+  user_prefs->RegisterStringPref(prefs::kExperimentalZeroSuggestUrlPrefix, "",
+                                 PrefService::UNSYNCABLE_PREF);
+}
+
 void ZeroSuggestProvider::Start(const AutocompleteInput& input,
                                 bool /*minimal_changes*/) {
   UpdateMatches(input.text());
 }
 
 void ZeroSuggestProvider::StartZeroSuggest(const GURL& url,
                                            const string16& user_text) {
   DCHECK(url.is_valid());
   // Do not query non-http URLs. There will be no useful suggestions for https
   // or chrome URLs.
@@ skipping 164 matching lines @@
     // Style to look like normal search suggestions.
     match.contents_class.push_back(
        ACMatchClassification(0, ACMatchClassification::DIM));
     match.contents_class.push_back(
        ACMatchClassification(user_text_.length(), ACMatchClassification::NONE));
   }
   match.transition = content::PAGE_TRANSITION_GENERATED;
 
   matches_.push_back(match);
 }