Perhaps their implementation differs, but they even showed the JS they're using to perform the prefetch in the post. It doesn't seem like they're trying to hide anything.
I'm curious what exact antitrust concept you think this violates.
For example, Microsoft performed a technique known as tying.
But even the claim was not simply "they shipped IE with Windows 98" , or that they introduced other product features to work well with IE first, but "they made IE deliberately difficult to remove, and deliberately and intentfully made it harder for netscape navigator to work". This is not the same as "we made IE the best, and did nothing to competitive products". In particular, it is not the fact that they introduced stuff to IE first, it is the fact that they deliberately harmed the other products.
See paragraphs 94, 95, and 96 on http://law.justia.com/cases/federal/appellate-courts/F3/253/...
Even then, the court held the tying should be analyzed deferentially, and that the US would have to prove this had actual anticompetitive effect.
See in particular, the court's admonition at 93
"As a general rule, courts are properly very skeptical about claims that competition has been harmed by a dominant firm's product design changes. See, e.g., Foremost Pro Color, Inc. v. Eastman Kodak Co., 703 F.2d 534, 544-45 (9th Cir. 1983). In a competitive market, firms routinely innovate in the hope of appealing to consumers, sometimes in the process making their products incompatible with those of rivals; the imposition of liability when a monopolist does the same thing will inevitably deter a certain amount of innovation. This is all the more true in a market, such as this one, in which the product itself is rapidly changing. See Findings of Fact p 59. Judicial deference to product innovation, however, does not mean that a monopolist's product design decisions are per se lawful. See Foremost Pro Color, 703 F.2d at 545; see also Cal. Computer Prods., 613 F.2d at 739, 744; In re IBM Peripheral EDP Devices Antitrust Litig., 481 F. Supp. 965, 1007-08 (N.D. Cal. 1979)."
Note that these are also tying between sold products and given away products, not just given away products. Otherwise, open source linux distributions with large market share would have tying issues (and in fact, they've been unsuccessfully sued for illegal competition before)
I think Google needs to check its steps quite carefully when doing things like these. For quite some time they have leveraged their search monopoly (think about their EU search market share) to bring search/browser-type integration features to chrome first. I would say this is abusing a monopoly in one market segment (search in the EU) to attempt to create a monopoly in another segment (browsers in the EU) by continually making sure that Chrome is the browser that works better than other browsers when using Google search services.
Yes, this is innovative, but there is also a concept known as antitrust laws. Another way of bringing this to the market would have been to invite competing browsers to use this and build a credible time plan for a simultaneous launch for all the browsers that wanted to support this.