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

chrome/common/chrome_features.cc

Index: chrome/common/chrome_features.cc
diff --git a/chrome/common/chrome_features.cc b/chrome/common/chrome_features.cc
index a3787180e8e2a569460279a09df2c2b9ce9831c6..a7643b349ff316fe7b55bfac6309d4c55f813212 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -22,6 +22,11 @@ const base::Feature kLinuxObsoleteSystemIsEndOfTheLine{
     "LinuxObsoleteSystemIsEndOfTheLine", base::FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
+// Enables or disables the Material Design version of chrome://history.
+const base::Feature kMaterialDesignHistoryFeature {
+  "MaterialDesignHistory", base::FEATURE_DISABLED_BY_DEFAULT
+};
+
 #if defined(OS_CHROMEOS)
 // Runtime flag that indicates whether this leak detector should be enabled in
 // the current instance of Chrome.