message: Improving error reporting in LogDump.
diff: @@ -536,12 +536,12 @@ void DumpGraphvizVideoFrame(const Model& model) {
  if (!dump_hashes.count(hash)) {
  LOG(INFO) << "DUMPING GRAPHVIZ VIDEO FRAME: " << dump_id;
  dump_hashes.insert(hash);
  - CHECK(port::file::SetContents(
  + const auto result = port::file::SetContents(
  port::file::JoinPath(
  dump_options.dump_graphviz,
  toco::port::StringF("toco_video_%05d.dot", dump_id)),
  - graphviz_dump, port::file::Defaults())
  - .ok());
  + graphviz_dump, port::file::Defaults());
  + QCHECK(result.ok()) << result.error_message();
  dump_id++;
  }
  }
  @@ -555,14 +555,13 @@ void LogDump(int log_level, const string& message, const Model& model) {
  string graphviz_dump;
  DumpGraphviz(model, &graphviz_dump);
  - CHECK(port::file::SetContents(
  + const auto result = port::file::SetContents(
  port::file::JoinPath(
  dump_options.dump_graphviz,
  - absl::StrCat("toco_",
  - absl::StrReplaceAll(message, {{" ", "_"}}),
  + absl::StrCat("toco_", absl::StrReplaceAll(message, {{" ", "_"}}),
  ".dot")),
  - graphviz_dump, port::file::Defaults())
  - .ok());
  + graphviz_dump, port::file::Defaults());
  + QCHECK(result.ok()) << result.error_message();
  }
  if (!VLOG_IS_ON(log_level)) {
  