CLC-4356 - Resolve issue with LTI tool iframe resizing

https://jira.ets.berkeley.edu/jira/browse/CLC-4356
@redconfetti can we make `document.getElementsByClassName('tool_content_wrapper')` a variable?
Should make the code it bit more readable.

Also, you can probably combine the 2 `if`s.

```
var toolContentWrapper = document.getElementsByClassName('tool_content_wrapper');
if (toolContentWrapper && toolContentWrapper.length && toolContentWrapper[0] && toolContentWrapper.style) {
...
```