you could try to use a special styled div with the contenteditable attribute (i do not know if this is working on webview). http://html5demos.com/contenteditable
But it looks so: http://caniuse.com/#search=contenteditable
The user can type in text --> and you could add something like bb-codes like it is here 
= :slightly_smiling:
so you can replace such codes with icons (regexps ftw^^)