Add media controls in media notification

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 1892 matching lines @@
       </message>
       <message name="IDS_ACCESSIBILITY_PLAY" desc="Content description for the play button that starts playing the media.">
         Play
       </message>
       <message name="IDS_ACCESSIBILITY_PAUSE" desc="Content description for the pause button that pauses playing the media.">
         Pause
       </message>
       <message name="IDS_ACCESSIBILITY_STOP" desc="Content description for the stop button that stops playing the media.">
         Stop
       </message>
+      <message name="IDS_ACCESSIBILITY_PREVIOUS_TRACK" desc="Content description for the previous track button that switchs media to the previous track.">
+        Previous track
+      </message>
+      <message name="IDS_ACCESSIBILITY_NEXT_TRACK" desc="Content description for the next track button that switchs media to the next track.">
+        Next track
+      </message>
 
       <!-- New Tab Page strings -->
       <message name="IDS_NTP_BOOKMARKS" desc="Text for bookmarks button [CHAR-LIMIT=20]">
         Bookmarks
       </message>
       <message name="IDS_RECENT_TABS" desc="Text for button to show 'Recent tabs', i.e. recently closed tabs and tabs that are open on other devices [CHAR-LIMIT=20]">
         Recent tabs
       </message>
       <message name="IDS_MOST_VISITED_PLACEHOLDER_TITLE" desc="Header text shown on the new tab page when there are no most visited tiles yet.">
         Nothing to see here… yet
@@ skipping 779 matching lines @@
       <message name="IDS_ITEM_CHOOSER_ITEM_NAME_WITH_ID" desc="To distinguish items with the same name, the item chooser shows the item name with id.">
         <ph name="ITEM_NAME">%1$s<ex>item_name</ex></ph> (<ph name="ITEM_ID">%2$s<ex>item id</ex></ph>)
       </message>
 
       <message name="IDS_INSTANT_APPS_OPEN_IN_APP" desc="Button label for the user action that will open an Instant App.">
         Open app
       </message>
     </messages>
   </release>
 </grit>