Finds uses of throwing exceptions usages in Objective-C files.

For the same reason as the Google C++ style guide, we prefer not throwing exceptions from Objective-C code.

The corresponding C++ style guide rule:

Instead, prefer passing in NSError ** and return BOOL to indicate success or failure.

A counterexample:

- (void)readFile {
  if ([self isError]) {
    @throw [NSException exceptionWithName:...];

Instead, returning an error via NSError ** is preferred:

- (BOOL)readFileWithError:(NSError **)error {
  if ([self isError]) {
    *error = [NSError errorWithDomain:...];
    return NO;
  return YES;

The corresponding style guide rule: