It is open source. The icon after a quick search: https://cs.chromium.org/chromium/src/third_party/skia/resour.... Unsure if it's the one that's, say, put in the Windows app manifest. Also unsure if the repo contains all the Chrome resources, but I was under the impression that it did.
https://chromium.googlesource.com/chromium/src/+/lkgr/docs/c... documents the differences on Linux (given it's the only platform which regularly has both packaged). That does seem to miss the EME CDM, though (I'd write a patch for it, but I'm a bit busy at the moment!).
Google Chrome isn't. Chromium is, but Chromium also tends to download 3rd party close-source blobs from online resources, like the one that turns on your microphone.
Based on the link you provided it looks like it's Opt-Out not Opt-In, so it's not really a bug so much as a "feature" that open source software shouldn't have but google wanted to sneak in. based on this link [0] it's pretty clear that they did this intentionally and only changed things after user outcry. I wouldn't call that a bug.
Sounds like the opt-out tracking Mozilla put in, or the advertisement for that TV show it spammed which did stupid things to text. It would be nice to have a mainstream browser which didn't try to track, advertise to, or shove "telemetry" into users.
It wasn't an ad. It shut down before init if you hadn't manually set an about:config value telling it to run.
It was set up in a dumb way, but people also grossly misreported. The extension was "enabled" by default but did exactly nothing except shut itself down. The behavior was all disabled by default.