message: in DependencyDescriptor writer do not leave remaing bits uninitialized
  Cr-Commit-Position: refs/heads/master@{#31282}
diff: @@ -74,6 +74,11 @@ bool RtpDependencyDescriptorWriter::Write() {
  WriteExtendedFields();
  WriteFrameDependencyDefinition();
  }
  + size_t remaining_bits = bit_writer_.RemainingBitCount();
  + if (remaining_bits > 0) {
  + // Zero remaining memory to avoid leaving it uninitialized.
  + WriteBits(/*val=*/0, remaining_bits);
  + }
  return !build_failed_;
  }
  