1. It uses Google DNS internally, bypassing system DNS.
2. First-run analytics to Google, new tab page analytics to Google.
3. Various built-in google services that phone home: Google Host Detector, Google URL Tracker, Google Cloud Messaging, Google Hotwording, Google Safe Browsing, WiveDine DRM, Google AutoFill, etc.
4. Update checks for all these components (the browser does not have update, but the rest does).
5. Countless accesses to Google, such as geo-location to find nearest Google server, ping probes for connectivity, etc. For a list of domains that are accessed by Chromium, see this regex used by the ungoogled-chromium project: https://github.com/Eloston/ungoogled-chromium/blob/30969fddf...
More info at https://github.com/Eloston/ungoogled-chromium/tree/30969fddf....
I see no problem with neither Chrome nor Firefox defaulting to Google search and suggestions, as that is easily configurable for normal users. All of the above, however, is not.