Improving PictureListener deprecating comments

Change-Id: If189823962c49db9681845996e97eec31fedcca6

Author: kristianmonsen

core/java/android/webkit/WebView.java

@@ -927,7 +927,11 @@ public interface PictureListener {
          * Notify the listener that the picture has changed.
          * @param view The WebView that owns the picture.
          * @param picture The new picture.
-         * @deprecated This method is now obsolete.
+         * @deprecated Due to internal changes, the picture does not include
+         * composited layers such as fixed position elements or scrollable divs.
+         * While the PictureListener API can still be used to detect changes in
+         * the WebView content, you are advised against its usage until a replacement
+         * is provided in a future Android release
          */
         @Deprecated
         public void onNewPicture(WebView view, Picture picture);