Revert "Use sendMessage() API in Chrome instead of sendRequest()"

This reverts commit d271e105686971a0f7a75c27c4d5f251d3358688.

Although the Chrome extension docs state that the chrome.runtime API
was introduced in Chrome 22. However, unbeknownst to me,
chrome.runtime.sendMessage() wasn't introduced until Chrome 26. Since
Ubuntu bundles Chromium 25, we have to use the old API.