UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/66.0.3359.181 Chrome/66.0.3359.181 Safari/537.36

Steps to reproduce the problem:
1. Create background script
2. Create manifest json
3. Turn on developer mode
4. Load unpacked extension

## background.js
```javascript
function hello() {
    console.log("hello world")
}

hello();
```

## manifest.json
```json
{
  "name": "Getting Started Example",
  "version": "1.0",
  "description": "Build an Extension!",
  "manifest_version": 2,

  "background": {
    "scripts": [
      "background.js"
    ]
  }
}
```

What is the expected behavior?
* Extension should be loaded without any errors
* 'hello word' should be printed to background page console

What went wrong?
* Error when extension is loaded

WebStore page: 

Did this work before? N/A 

Chrome version: 66.0.3359.181  Channel: stable
OS Version: Linux mint 18.3
Flash Version: 

Even though there are errors, console log is printed successfully.
 

Deleted: sample ext.zip 670 bytes

sample ext.zip 670 bytes Download

Deleted: screenshot.png 19.2 KB

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