I currently use two external monitors with my MacBook Air – one connected via the mini displayport, the second via a USB graphics card. When using google hangouts in chrome, on either the laptop screen, or the first external monitor, any chrome windows open on the second external monitor would flicker like crazy. This was especially problematic for a typical layout / work-flow for me: hangout on large screen, relevant doc for the conversation open to the side on the USB monitor.
It turns out there’s an easy fix:
Go to chrome://flags/ and enable “GPU compositing on all pages” then click restart at the bottom of the screen.
I’m posting this because it was relatively hard to find a solution, so I’m hoping this post will include enough of the keywords I tried when looking for a fix to show up for others in searches. You’re welcome.