Address Broadcast Radio HAL review notes.

Bug: b/64229617
Test: instrumentation, VTS
Change-Id: I4009b33eaea6df585f514711f22dfb7fec5ad379
diff --git a/broadcastradio/1.1/IBroadcastRadio.hal b/broadcastradio/1.1/IBroadcastRadio.hal
index 9bde361..6e7002d 100644
--- a/broadcastradio/1.1/IBroadcastRadio.hal
+++ b/broadcastradio/1.1/IBroadcastRadio.hal
@@ -40,6 +40,19 @@
      * The data should be a valid PNG, JPEG, GIF or BMP file.
      * Invalid format must be handled gracefully as if the image was missing.
      *
+     * The image identifier may become invalid after some time from passing it
+     * with metadata struct (due to resource cleanup at the HAL implementation).
+     * However, it must remain valid for a currently tuned program at least
+     * until currentProgramInfoChanged or programListChanged is called and
+     * metadata changes for the current program.
+     *
+     * There is still a race condition possible (if the HAL deletes the old
+     * image immediately after notifying about the new one) between
+     * currentProgramInfoChanged callback propagating through the framework and
+     * the HAL implementation removing previous image. In such case, client
+     * application may expect the new currentProgramInfoChanged callback with
+     * updated image identifier.
+     *
      * @param id Identifier of an image;
      *           value of 0 is reserved and should be treated as invalid image.
      * @return image A binary blob with image data