Steps to test the change:
* Open a random page in browser.
* Select all or a part of the page.
* Copy the selection to clipboard.
* Open a word processor like LibreOffice Writer.
* Paste the content of the clipboard.
Change-Id: Ibae4292b5dd8cc02a769e85adfea991d8d6ceb59
Had to do that in JavaScript as doing it server-side would have
made refactoring large parts of the extension necessary.
Bug: 38141
Change-Id: I60ecd2fc0edf2aee89974d8069cc0b075cda3f93