Reland fast tab closure behind a flag

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 138 matching lines @@
 extern const char kEnableAutologin[];
 extern const char kEnableBenchmarking[];
 extern const char kEnableCloudPrintProxy[];
 extern const char kEnableComponentCloudPolicy[];
 extern const char kEnableContacts[];
 extern const char kEnableDesktopGuestMode[];
 extern const char kEnableDevToolsExperiments[];
 extern const char kEnableExperimentalExtensionApis[];
 extern const char kEnableExtensionActivityLogging[];
 extern const char kEnableExtensionActivityLogTesting[];
+extern const char kEnableFastUnload[];
 extern const char kEnableFileCookies[];
 extern const char kEnableGoogleNowIntegration[];
 extern const char kEnableInstantExtendedAPI[];
 extern const char kEnableIPCFuzzing[];
 extern const char kEnableIPPooling[];
 extern const char kEnableIPv6[];
 extern const char kEnableLocalFirstLoadNTP[];
 extern const char kEnableManagedStorage[];
 extern const char kEnableManagedUsers[];
 extern const char kEnableMemoryInfo[];
@@ skipping 283 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_