I want to preface this with a warning that this is 100% conjecture. Literally none of this has any proof...I personally don't think chrome has anything "up their sleeve". From the looks of what they have been focusing on recently, they really dug themselves a hole with their technical debt in the V8 engine.
It's too complicated, and it looks like their upgrade path has it getting worse before it gets better. They aren't planning on switching to "Ignition -> Turbofan" until mid-late 2017 (which is expected to reduce memory usage, but also will reduce speed slightly at first), so that means that until then, it will be "Fullcodegen -> crankshaft or turbofan and sometimes ignition only in some codepaths". It's only getting more complicated as they try to write out their crankshaft compiler. IIRC ignition can't interface with cranshaft, while it can with turbofan, but turbofan is significantly slower than cranshaft for many things right now, and fullcodegen is WAY to slow in parsing (and re-parsing, and re-re-parsing) code to compete with Chakra which just starts SOO much faster because of that.
On the non-javascript side, servo is proving to be a MASSIVE amount of work, and I honestly don't think that blink is going to be able to be retrofitted easily to get similar gains. And nobody has heard a peep about a "secret new web engine being developed at google", so I really don't think they have one (or if they do, it's still a few years out at best).
I love chrome, but it's not in a good position. Edge is consistently faster in javascript execution, Safari is significantly better to the battery (if missing a pretty large chunk of newer features), and when Firefox starts integrating Servo, they are going to be king of layout/painting/rendering speeds (which is by far one of the biggest bottlenecks in modern web apps).
I hope they prove me wrong, but my hopes aren't high at this time.