Using IME with markdown preview enabled, press ESC/BACKSPACE leads in control characters

[timonwong]

• VSCode Version: 1.17.2
• OS Version: macOS 10.11.6

Steps to Reproduce:

HINT: You may need to enable editor.renderControlCharacters in order to see what happens, or the control characters is invisible.

1. Open a "markdown preview" in a split (just ensure the markdown preview is visible).
2. In another split, edit arbitrary file with IME (mine with Chinese Pinyin).
3. Type some characters using IME, before put them on screen, type backspace/esc to see what happens.

Just see the screenshot for example:

Reproduces without extensions: Yes

[rebornix]

It only happens when you are previewing the markdown content, which means it's caused by the webview.

[rebornix]

It turns out that when we preview the md content, the webview will lead to the problem as described in #24981 (you need to double backspace to delete characters). This problem was introduced in Electron 1.5.x, fixed by backporting in 1.6.x, apparently they forgot to backport the fix in 1.7.x. Ideally this can be fixed once we adopt 1.8.x.

More info electron/electron#9173 (comment) , cc @bpasero @Tyriar