Spellchecker regression in v3.x

[fxha]

• Output of node_modules/.bin/electron --version: v3.1.1 (maybe v4.0.x too)
• Operating System (Platform and Version): Linux 4.19.x
• Output of node_modules/.bin/electron --version on last known working Electron version (if applicable): v2.0.16

Expected Behavior

Spell checking should always work and highlight all misspelled words in a textarea and contenteditable block.

Actual behavior

Spell checking only works for short text lines. If you use longer lines or words, only the selected line is red highlighted.

To Reproduce

$ git clone https://github.com/fxha/electron-3-spellcheck
$ npm install
$ npm run start

Screenshots

Additional Information

#13608 was a similar issue.

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[nornagon]

This matches Chrome's behaviour and is working as expected.