Problem:
iPhone 6 Plus is considered a tablet.
Expected behavior:
It's a phone.
Root cause:
In `resources/mobile.browser/browser.js`:
```isWideScreen: memoize(function() {
var val = parseInt(mw.config.get('wgMFDeviceWidthTablet'), 10);
return window.innerWidth >= val || window.innerHeight >= val;
})```
`wgMFDeviceWidthTablet` is '720px'
The height of iPhone 6 Plus is 736.
Since we check both portrait and landscape mode, the threshold should be the long edge instead of width. Adding one more config variable called `wgMFDeviceLongEdgeTablet` or `wgMFDeviceHeightTablet` might make sense. Or just derive from `wgMFDeviceWidthTablet` * 4/3 (aspect ratio).
According to http://mydevice.io/devices/, 800px looks like a good threshold for the long edge measure.
This issue is discovered in https://bugs.chromium.org/p/chromium/issues/detail?id=647667#c14 because section collapsing is determined by whether it's a phone or tablet.
= Acceptance criteria
[] From now on we should only check **the width** of the device.
```
isWideScreen: memoize(function() {
var val = parseInt(mw.config.get('wgMFDeviceWidthTablet'), 10);
return window.innerWidth >= val;
})
```
[] Add some documentation explaining that we do not check the height to avoid situations where tablet and mobile modes differ.