Add a class Javadoc for MediaBrowser.MediaItem

Also fixed a typo in MediaBrowserService.

Bug: 26181781, Bug: 26182458
Change-Id: I1f672f8111a70ad9c16e9969d0fad0e504fefb8a

media/java/android/media/browse/MediaBrowser.java

@@ -574,6 +574,9 @@ public final class MediaBrowser {
         Log.d(TAG, "  mMediaSessionToken=" + mMediaSessionToken);
     }
 
+    /**
+     * A class with information on a single media item for use in browsing media.
+     */
     public static class MediaItem implements Parcelable {
         private final int mFlags;
         private final MediaDescription mDescription;

media/java/android/service/media/MediaBrowserService.java

@@ -546,7 +546,7 @@ public abstract class MediaBrowserService extends Service {
         }
 
         /**
-         * Gets any extras about the brwoser service.
+         * Gets any extras about the browser service.
          */
         public Bundle getExtras() {
             return mExtras;