Comment by Tepix

According to https://www.google.com/chrome/privacy/whitepaper.html

"We want to build features that users want, so a subset of users may get a sneak peek at new functionality being tested before it’s launched to the world at large. A list of field trials that are currently active on your installation of Chrome will be included in all requests sent to Google. This Chrome-Variations header (X-Client-Data) will not contain any personally identifiable information, and will only describe the state of the installation of Chrome itself, including active variations, as well as server-side experiments that may affect the installation."

While this header may not contain personally identifiable information, its presence will make every request by this user far more unique and thus easier to track. I do not see Google saying they won't use it to improve their tracking of people.