Control zero suggest with a pref, not a switch.

chrome/common/chrome_switches.h

 // 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.
 
 // Defines all the command-line switches used by Chrome.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
 #include "build/build_config.h"
@@ skipping 169 matching lines @@
 extern const char kEnableSpdyFlowControl[];
 extern const char kEnableStackedTabStrip[];
 extern const char kEnableSuggestionsTabPage[];
 extern const char kEnableTabGroupsContextMenu[];
 extern const char kEnableTextServiceFramework[];
 extern const char kEnableWatchdog[];
 extern const char kEnableWebSocketOverSpdy[];
 extern const char kEventPageIdleTime[];
 extern const char kEventPageUnloadingTime[];
 extern const char kExperimentalSpellcheckerFeatures[];
-extern const char kExperimentalZeroSuggestURLPrefix[];
 extern const char kExplicitlyAllowedPorts[];
 extern const char kExtensionProcess[];
 extern const char kExtensionsUpdateFrequency[];
 extern const char kExternalAutofillPopup[];
 extern const char kFlagSwitchesBegin[];
 extern const char kFlagSwitchesEnd[];
 extern const char kFeedbackServer[];
 extern const char kFileDescriptorLimit[];
 extern const char kFirstRun[];
 extern const char kGaiaProfileInfo[];
@@ skipping 248 matching lines @@
 #else
 extern const char kEnablePrintPreview[];
 #endif
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace switches
 
 #endif  // CHROME_COMMON_CHROME_SWITCHES_H_