Convert --enable-md-history to a feature flag.

chrome/browser/about_flags.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/about_flags.h"
 
 #include <iterator>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 1689 matching lines @@
      IDS_FLAGS_HERB_PROTOTYPE_CHOICES_DESCRIPTION, kOsAndroid,
      MULTI_VALUE_TYPE(kHerbPrototypeChoices)},
     {"enable-tab-switcher-in-document-mode",
      IDS_FLAGS_TAB_SWITCHER_IN_DOCUMENT_MODE_NAME,
      IDS_FLAGS_TAB_SWITCHER_IN_DOCUMENT_MODE_DESCRIPTION, kOsAndroid,
      SINGLE_VALUE_TYPE(switches::kEnableTabSwitcherInDocumentMode)},
 #endif  // OS_ANDROID
     {"enable-md-history", IDS_FLAGS_ENABLE_MATERIAL_DESIGN_HISTORY_NAME,
      IDS_FLAGS_ENABLE_MATERIAL_DESIGN_HISTORY_DESCRIPTION,
      kOsDesktop,
-     SINGLE_VALUE_TYPE(switches::kEnableMaterialDesignHistory)},
+     FEATURE_VALUE_TYPE(switches::kMaterialDesignHistoryFeature)},
 #if defined(OS_WIN)
     {"enable-windows-desktop-search-redirection",
      IDS_FLAGS_WINDOWS_DESKTOP_SEARCH_REDIRECTION_NAME,
      IDS_FLAGS_WINDOWS_DESKTOP_SEARCH_REDIRECTION_DESCRIPTION, kOsWin,
      FEATURE_VALUE_TYPE(kDesktopSearchRedirectionFeature)},
 #endif  // defined(OS_WIN)
     {"force-ui-direction", IDS_FLAGS_FORCE_UI_DIRECTION_NAME,
      IDS_FLAGS_FORCE_UI_DIRECTION_DESCRIPTION, kOsAll,
      MULTI_VALUE_TYPE(kForceUIDirectionChoices)},
 #if defined(ENABLE_EXTENSIONS)
@@ skipping 283 matching lines @@
 const base::HistogramBase::Sample kBadSwitchFormatHistogramId = 0;
 
 const FeatureEntry* GetFeatureEntries(size_t* count) {
   *count = arraysize(kFeatureEntries);
   return kFeatureEntries;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags