[NTP Snippets] Make a base::Feature instead of raw cmdline flag

chrome/android/java/src/org/chromium/chrome/browser/ChromeFeatureList.java

 // Copyright 2015 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.
 
 package org.chromium.chrome.browser;
 
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.MainDex;
 
 /**
@@ skipping 11 matching lines @@
      * Note: Features queried through this API must be added to the array
      * |kFeaturesExposedToJava| in chrome/browser/android/chrome_feature_list.cc
      *
      * @param featureName The name of the feature to query.
      * @return Whether the feature is enabled or not.
      */
     public static boolean isEnabled(String featureName) {
         return nativeIsEnabled(featureName);
     }
 
+    public static final String NTP_SNIPPETS = "NTPSnippets";
+
     private static native boolean nativeIsEnabled(String featureName);
 }