aggregator: add gst_aggregator_pad_drop_buffer()

steal_buffer() + unref seems to be a wide-spread idiom
(which perhaps indicates that something is not quite
right with the way aggregator pad works currently).

docs/libs/gst-plugins-bad-libs-sections.txt

@@ -1323,6 +1323,8 @@ GstAggregatorPad
 GstAggregatorPadClass
 gst_aggregator_pad_steal_buffer
 gst_aggregator_pad_get_buffer
+gst_aggregator_pad_drop_buffer
+gst_aggregator_pad_is_eos
 <SUBSECTION Standard>
 GST_IS_AGGREGATOR_PAD
 GST_IS_AGGREGATOR_PAD_CLASS

gst-libs/gst/base/gstaggregator.c

@@ -2062,6 +2062,28 @@ gst_aggregator_pad_steal_buffer (GstAggregatorPad * pad)
   return buffer;
 }
 
+/**
+ * gst_aggregator_pad_drop_buffer:
+ * @pad: the pad where to drop any pending buffer
+ *
+ * Drop the buffer currently queued in @pad.
+ *
+ * Returns: TRUE if there was a buffer queued in @pad, or FALSE if not.
+ */
+gboolean
+gst_aggregator_pad_drop_buffer (GstAggregatorPad * pad)
+{
+  GstBuffer *buf;
+
+  buf = gst_aggregator_pad_steal_buffer (pad);
+
+  if (buf == NULL)
+    return FALSE;
+
+  gst_buffer_unref (buf);
+  return TRUE;
+}
+
 /**
  * gst_aggregator_pad_get_buffer:
  * @pad: the pad to get buffer from

gst-libs/gst/base/gstaggregator.h

@@ -104,6 +104,7 @@ GType gst_aggregator_pad_get_type           (void);
 
 GstBuffer * gst_aggregator_pad_steal_buffer (GstAggregatorPad *  pad);
 GstBuffer * gst_aggregator_pad_get_buffer   (GstAggregatorPad *  pad);
+gboolean    gst_aggregator_pad_drop_buffer  (GstAggregatorPad *  pad);
 gboolean    gst_aggregator_pad_is_eos       (GstAggregatorPad *  pad);
 
 /*********************