Reland "Adding media controls to MediaNotification"

content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java

Index: content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
diff --git a/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java b/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
index 5e03463b9a29bbf9a5226e19632270544cd57a23..b133f883f20dfd51b70d22c29f5589fa354fccd3 100644
--- a/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
+++ b/content/public/android/java/src/org/chromium/content_public/browser/MediaSessionObserver.java
@@ -56,6 +56,18 @@ public abstract class MediaSessionObserver {
     public void mediaSessionMetadataChanged(MediaMetadata metadata) {}
 
     /**
+     * Called when the observed {@link MediaSession} has enabled an action.
+     * @param action The enabled action.
+     */
+    public void mediaSessionEnabledAction(int action) {}
+
+    /**
+     * Called when the observed {@link MediaSession} has disabled an action.
+     * @param action The disabled action.
+     */
+    public void mediaSessionDisabledAction(int action) {}
+
+    /**
      * Stop observing the media session. Users must explicitly call this before dereferencing the
      * observer.
      */