"SyntaxError: Unexpected identifier" in webview

[borisyankov]

https://sentry.io/zulip/zulip-mobile/issues/554709208/

Error: {"message":"Uncaught SyntaxError: Unexpected identifier","source":"https://chat.zulip.org/","line":1,"column":212137,"error":{}}
    at src/webview/webViewEventHandlers.toUpperCase(webViewEventHandlers.js:172)
    logErrorRemotely(new Error(JSON.stringify(event.details)), 'WebView Exception');
    at src/webview/MessageListWeb.this(MessageListWeb.js:40)
    const handler = `handle${eventData.type.charAt(0).toUpperCase()}${eventData.type.slice(1)}`;
...
(13 additional frame(s) were not displayed)

[gnprice]

More details in #2640 from @adambirds, who ran into an instance of this issue.