The keyDown/keyUp paths interpolated `key`/`code` into the generated
KeyboardEvent snippet with single-quote escaping only. Chrome sends
`key: "\"` (U+005C) for the backslash key, which became `key:'\'` — the
backslash escaped the closing quote, ran the string literal on, and made
the whole page.evaluate a syntax error, so the keydown was silently
dropped. Any key/code carrying a backslash broke dispatch.
Escape backslash before single-quote (backslash first, so the quote-escape
backslashes are not themselves doubled), matching the sibling text path in
the same function. Adds a regression test asserting the backslash key
arrives at a keydown listener alongside an ordinary key.
Andrey Mnatsakanov
57949a0efc