I have developed this Singlish Real-time transliteration extension for Chrome
I have set all users of this group as test accounts. You may download and review this extension.
Once you install this, an icon "සි" on the top right corner of the page.
When you hover on the icon, a drop down should appear. Select transliteration/encoding you want, and then you can type Sinhala then and there, no need to copy and paste.