message: check_format: improved error behavior
  If you forget to pass "check" or "fix" as the first argument, print an
  error instead of doing nothing and silently exit(0)ing.
diff: @@ -5,6 +5,8 @@ import os
  import os.path
  import sys
  +USAGE = "usage: check_format.py <check|fix> [<directory|file>]"
  +
  EXCLUDED_PREFIXES = ("./generated/", "./thirdparty/", "./build", "./.git/",
  "./bazel-")
  SUFFIXES = (".cc", ".h", "BUILD")
  @@ -93,12 +95,16 @@ def checkFormatVisitor(arg, dir_name, names):
  if __name__ == "__main__":
  if len(sys.argv) != 2 and len(sys.argv) != 3:
  - print("usage: check_format.py <check|fix> [<directory|file>]")
  + print(USAGE)
  sys.exit(1)
  operation_type = sys.argv[1]
  target_path = sys.argv[2] if len(sys.argv) == 3 else "."
  + if operation_type not in {"check", "fix"}:
  + print(USAGE)
  + sys.exit(1)
  +
  if os.path.isfile(target_path):
  checkFormat("./" + target_path)
  else:
  