chrome/blink: Add functionality for in-product help for media elements.

components/feature_engagement/public/android/java/src/org/chromium/components/feature_engagement/EventConstants.java

 // Copyright 2017 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.components.feature_engagement;
 
 /**
  * EventConstants contains the String name of all in-product help events.
  */
 public final class EventConstants {
@@ skipping 43 matching lines @@
      */
     public static final String OVERFLOW_OPENED_WITH_DATA_SAVER_SHOWN =
             "overflow_opened_data_saver_shown";
 
     /**
      * The data saver footer was used (tapped).
      */
     public static final String DATA_SAVER_DETAIL_OPENED = "data_saver_overview_opened";
 
     /**
+     * The download button for a media element was displayed.
+     */
+    public static final String MEDIA_DOWNLOAD_BUTTON_DISPLAYED = "media_download_button_displayed";
+
+    /**
      * Do not instantiate.
      */
     private EventConstants() {}
 }