Google Fonts returning "local('sans-serif')" before "Roboto*" URL's if user-agent includes Android > 4.0

### Steps to reproduce

Set user-agent to: `Mozilla/5.0 (Linux; Android 5.0; SM-G892A Build/NRD90M; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/67.0.3396.87 Mobile Safari/537.36`

Load URL: `https://fonts.googleapis.com/css?family=Roboto%3A300%2C400%2C700`

#### Actual result
"local('sans-serif')" is preceding the URL of the Font-File using the sans-serif font if installed on system.
```
...
/* latin */
@font-face {
font-family: 'Roboto';
font-style: normal;
font-weight: 400;
src: local('Roboto'), local('Roboto-Regular'), local('sans-serif'), url(https://fonts.gstatic.com/s/roboto/v19/KFOmCnqEu92Fr1Mu4mxKKTU1Kg.woff2) format('woff2');
unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
}
...
```
#### Expected result

local('sans-serif') should be omitted in result.

---

Setting the Android version to 4.0 (or lower) or exclude Android completely the "local('sans-serif')" is omitted.

```
/* latin */
@font-face {
font-family: 'Roboto';
font-style: normal;
font-weight: 400;
src: local('Roboto'), local('Roboto-Regular'), url(https://fonts.gstatic.com/s/roboto/v19/KFOmCnqEu92Fr1Mu4mxK.woff2) format('woff2');
unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
}
```

The problem is reproducable for me with all browsers (Chrome, Chromium, Firefox, Opera ...) on all platforms (Windows ..., Linux).