[MD Settings] Add feature to enable md-settings by default.

chrome/common/chrome_features.h

 // Copyright 2016 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.
 
 // This file defines all the public base::FeatureList features for the chrome
 // module.
 
 #ifndef CHROME_COMMON_CHROME_FEATURES_H_
 #define CHROME_COMMON_CHROME_FEATURES_H_
 
@@ skipping 23 matching lines @@
 #if defined(OS_CHROMEOS)
 extern const base::Feature kHappininessTrackingSystem;
 #endif
 
 #if defined(GOOGLE_CHROME_BUILD) && defined(OS_LINUX) && !defined(OS_CHROMEOS)
 extern const base::Feature kLinuxObsoleteSystemIsEndOfTheLine;
 #endif
 
 extern const base::Feature kMaterialDesignHistoryFeature;
 
+extern const base::Feature kMaterialDesignSettingsFeature;
+
 #if defined(OS_CHROMEOS)
 extern const base::Feature kRuntimeMemoryLeakDetector;
 #endif  // defined(OS_CHROMEOS)
 
 extern const base::Feature kSafeSearchUrlReporting;
 
 extern const base::Feature kSimplifiedFullscreenUI;
 
 #if defined(SYZYASAN)
 extern const base::Feature kSyzyasanDeferredFree;
 #endif
 
 #if defined(OS_CHROMEOS)
 extern const base::Feature kOptInImeMenu;
 #endif  // defined(OS_CHROMEOS)
 
 // 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 features
 
 #endif  // CHROME_COMMON_CHROME_FEATURES_H_