ImageReader: Make discardFreeBuffers public

Test: CTS
Bug: 64847201
Change-Id: I61008111552b5ca4641a509e5bcf5cf821582d5e
diff --git a/api/current.txt b/api/current.txt
index c1188dc..a9d1882 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -22028,6 +22028,7 @@
     method public android.media.Image acquireLatestImage();
     method public android.media.Image acquireNextImage();
     method public void close();
+    method public void discardFreeBuffers();
     method public int getHeight();
     method public int getImageFormat();
     method public int getMaxImages();
diff --git a/media/java/android/media/ImageReader.java b/media/java/android/media/ImageReader.java
index c78c99f..1019580 100644
--- a/media/java/android/media/ImageReader.java
+++ b/media/java/android/media/ImageReader.java
@@ -640,7 +640,6 @@
      * The ImageReader continues to be usable after this call, but may need to reallocate buffers
      * when more buffers are needed for rendering.
      * </p>
-     * @hide
      */
     public void discardFreeBuffers() {
         synchronized (mCloseLock) {