[Fuchsia] Fix DCHECK in FuchsiaVideoDecoder

FuchsiaVideoDecoder::ReleaseInputBuffers() was clearing
in_flight_input_packets_ before destroying input packets, which was
resulting in DCHECK failure. This change updates ReleaseInputBuffers()
to destroy input buffers before dropping the packets.

Bug: 1013919
Change-Id: I7288c1c47ab400877e5e4ec629083963b8e90a26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1857712
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705595}

media/filters/fuchsia/fuchsia_video_decoder.cc

@@ -1032,11 +1032,15 @@ void FuchsiaVideoDecoder::InitializeOutputBufferCollection(
 }
 
 void FuchsiaVideoDecoder::ReleaseInputBuffers() {
-  in_flight_input_packets_.clear();
   input_writer_queue_.ResetBuffers();
   input_buffer_collection_creator_.reset();
   input_buffer_collection_.reset();
   num_input_buffers_ = 0;
+
+  // |in_flight_input_packets_| must be destroyed after
+  // |input_writer_queue_.ResetBuffers()|. Otherwise |input_writer_queue_| may
+  // call SendInputPacket() in response to the packet destruction callbacks.
+  in_flight_input_packets_.clear();
 }
 
 void FuchsiaVideoDecoder::ReleaseOutputBuffers() {