Hmm, that sounds odd. Does the new tab lead to any website, or does it look like the normal "New Tab"? If it's the latter, try re-installing Chrome. The browser may be affected by some changes by a now gone virus. If that doesn't help, I'm thinking this may be a Trojan Horse, spyware, or a deeply-burrowed virus of some sort, which is why Malwarebytes isn't finding it. I suggest using Spybot Search and Destroy, or another security suite, just to ensure that Chrome and Malwarebytes were not tampered with.