Missing chrome.runtime

Chrome has a bunch of non-standard APIs exposed off of `chrome.runtime`. I [see](http://web-confluence.appspot.com/#!/catalog?releaseKeys=%5B%22Safari_11.0_OSX_10.12.6%22,%22Chrome_61.0.3163.79_Windows_10.0%22,%22Firefox_55.0_Windows_10.0%22,%22Edge_15.15063_Windows_10.0%22%5D&releaseOptions=null&numAvailable=null¤tPage=0&gap=5&itemPerPage=15&searchKey=%22chrome%22) the other properties on `chrome`, but not `runtime`. Any idea why? It looks to be exposed similarly to `chrome.webstore`.