Dude. Google indexes everything. You believe Chrome bookmark syncing would somehow be off limits?
Microsoft is running an ad right now ripping on Google for indexing keywords in peoples' Gmail for use in targeted advertising. "Don't be evil", my arse!
Let me ask you the opposite question: What proof do you have that Google isn't tracking synced bookmarks in Chrome?
Google indexes everything? Really? They even index what you turn off?
Those keywords are automated, though with any company you have email through they can read your email if they really wanted to. Doesn't make it right for anyone.
I don't, but I block all forms of tracking, ads, and other such nonsense, so they're wasting their money and time with me.
Seriously? Google is an advertising company. Unlike with Apple, you are not the customer. You are the product. Google's whole business model is to get as much information about you as possible to offer that to advertisers. It does that by giving you so called free product.
Yes, they are an advertising company. They're also a search company. If you think companies besides Google aren't also interested in learning about you, you're also wrong. But you being the product? No. If I learn you like mangos, and I show you mango ads, that doesn't make you a product.
But good luck with them showing me any ads. As I've said, I block them.
First, I have Little Snitch installed on my Mac. When using Chrome, it calls home multiple times a session. No other browser does that. By comparison, Safari and Firefox call home once a week to check for an update, and that can be shut off. Chrome is calling home to give Google your browsing information.
Do you know precisely what Chrome is sending to Google? Do you have proof for your assertion?
Second, Gmail scans your email and gives you ads based on what you send and receive in terms of email. For instance, I am a bankruptcy attorney. I get email with the words attorney and bankruptcy in them a lot. Consequently, Google gives me law school and bankruptcy attorney ads. This also highlights how Google's methods performs poorly for their real customers: the advertisers. I get ads from Google that I have no interest in.
I get no ads from Gmail whatsoever. Perhaps you need to do a better job of adblocking.
Third, Google's analytics definitely tracks your bookmarks.
If you don't disable it, it even does it on other browsers.
Meh, I've disabled that. I disabled everything I didn't care for. Tracking
can be useful, especially for companies looking to see how successful their advertising is. It isn't inherently evil.
Finally, I don't have any direct proof that if I take a nose dive off the twenty story water tower by my house I am going to die, but common sense dictates that is the case. The same applies with Google. Its business model requires it to data mine you. This might not bother you. There are larger principles at stake though related to government. Google has to give governments the information it has on you when the government requests it.
It's also refused to give out information when, for example, the US government has requested it. I don't give Google anything that I don't want to, so the information they have on me (which is pretty limited) doesn't bother me.
Further, Google's security isn't that great. Recently, the Wiki Leaks revealed that the Chinese government hacked Gmail and obtained a large amount of information. My step dad's account was recently hacked. I received emails from his actual email account telling me he was in the hospital. My gmail account was also hacked a few months later.
The Chinese are hacking all sorts of databases worldwide–Google simply happens to be a very large and valuable target to hit. Implying that because the Chinese hacked them makes them insecure is fallacious. They've hit secure military networks–does that make the military insecure, or just the Chinese very determined?
Google is not intrinsically evil. Sure, it's a corporation, and it wants to sell things, but it's not terribly difficult to block them from showing you ads or tracking you. I've done that, which is why I have no problem with Chrome.
hexor and scaredpoet also make good points.
The Peacekeeper benchmark is a strange one, not many see it as a good benchmark. The Kraken benchmark is one from Mozilla and has a slight bias towards Firefox. And we can go on and on like this. The differences you do see are very small and probably not even worth mentioning. 
