MacOSX 10.11.x (maybe all platforms, not sure)
52.0.2724.0 canary (happens in M51beta as well)

- create a new incognito tab.

The content area flashes white before painting the black background of the incognito NTP. This is very visible now since the material look for incognito is a totally dark window. 

To ccameron for now, please feel free to find a different owner. I'd like this for M52. It happens today, it's not a regression, but it's very jarring and will only be even more so when we launch MD on Mac.