Convert --enable-md-history to a feature 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 the shared command-line switches used by code in the Chrome
 // directory that don't have anywhere more specific to go.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
@@ skipping 104 matching lines @@
 extern const char kEnableClearBrowsingDataCounters[];
 extern const char kEnableCloudPrintProxy[];
 extern const char kEnableDevToolsExperiments[];
 extern const char kEnableDeviceDiscoveryNotifications[];
 extern const char kEnableDomainReliability[];
 extern const char kEnableExperimentalHotwordHardware[];
 extern const char kEnableExtensionActivityLogging[];
 extern const char kEnableExtensionActivityLogTesting[];
 extern const char kEnableFastUnload[];
 extern const char kEnableMaterialDesignExtensions[];
-extern const char kEnableMaterialDesignHistory[];
 extern const char kEnableMaterialDesignPolicyPage[];
 extern const char kEnableNaCl[];
 extern const char kEnableNativeNotifications[];
 extern const char kEnableNavigationTracing[];
 extern const char kEnableNetBenchmarking[];
 extern const char kEnableNewBookmarkApps[];
 extern const char kEnableNTPPopularSites[];
 extern const char kEnableNTPSearchEngineCountryDetection[];
 extern const char kEnableOfflineAutoReload[];
 extern const char kEnableOfflineAutoReloadVisibleOnly[];
@@ skipping 259 matching lines @@
 extern const char kEnableWaylandServer[];
 #endif
 
 #if defined(OS_WIN) || defined(OS_LINUX)
 extern const char kEnableInputImeAPI[];
 extern const char kDisableInputImeAPI[];
 #endif
 
 bool AboutInSettingsEnabled();
 bool MdExtensionsEnabled();
-bool MdHistoryEnabled();
 bool MdPolicyPageEnabled();
 bool PdfMaterialUIEnabled();
 bool SettingsWindowEnabled();
 
 #if defined(OS_CHROMEOS)
 bool PowerOverlayEnabled();
 #endif
 
 #if defined(ENABLE_TASK_MANAGER)
 bool NewTaskManagerEnabled();
 #endif  // defined(ENABLE_TASK_MANAGER)
 
 // 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_