Similar to bug 621512, which focuses on removing the chrome.loadTimes API, we should also remove the chrome.csi API. This API is non-standard, and even less intuitive than the chrome.loadTimes API. It also reports bad data, for instance, chrome.csi().onloadT reports not the onload time, but rather dom content loaded time. This is not documented anywhere, so any devs using onloadT for time to onload are getting bad data without realizing it.

We should deprecate this API and migrate developers to standard equivalent APIs.

As a first step, we should measure usage of this API. The API can be found here:

https://cs.chromium.org/chromium/src/chrome/renderer/loadtimes_extension_bindings.cc?q=getcsi&sq=package:chromium&l=60