UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/11.1.2 Safari/605.1.15

Steps to reproduce the problem:
1. On Win10, open up 3 windows in Chrome v56 or later running any webGL scene like  http://webglsamples.org/spacerocks/spacerocks.html and note the per windows FPS (around 60fps); open up a 4th window and watch the FPS for each window drop markedly (e.g 45fps)
2. Open up the same 3 windows using another browser on Win10 (like Firefox) and notice that there is no difference in in FPS of 4 windows vs. 3 windows when a 4th window is added
3. Open up same 3 windows on SAME version of Chrome but on MacOS or Linux and notice per windows FPS doesn't meaningfully change using 4 vs 3 windows
6. Open up same 3 windows of Chrome on v53 or earlier on Win10 and go from 3 windows to 4 and notice  per windows FPS doesn't meaningfully change using 4 vs 3 windows

What is the expected behavior?
The expected behavior is that for versions of Chrome >=56 on Win10 there should be no drops in frame rates when running 4 windows at once. The expected behavior IS the observed behavior if use (1) uses an earlier version of Chrome like v53 on same WIn10 OS (2) use a different browser on same Win10 OS like Firefox (3) uses same version of Chrome (including those >v56) on Linux or MacOS

What went wrong?
SO, something happens when going to v56 or later on Chrome on Windows only (only tested v10 or Windows) wherein per window frame rates fall hugely when going from 3 to 4 or more windows.  The problem only occurs with Win10 (not MacOS or Linux running on same hardware) and only on versions of Chrome greater or equal than v53

Did this work before? N/A 

Chrome version: <Copy from: 'about:version'>  Channel: n/a
OS Version: Win10
Flash Version: 

I am developing an electron app that uses multiple simultaneous windows...this is why I care. I was able to reproduce problem using just regular chrome browser with multiple windows open which is why I'm submitting bug here.

 recall: no performance degradation at all on Win10 Firefox or Chrome+Mac/Linux or on Win10 Chrome53 or earlier. It's not my hardware or system that's the problem (I'm using GTX1080 card with 10 core processor and taskmanager shows low utilizations) I've scoured web & Chrome release notes+flags. It's almost like the behavior in an intentional feature introduced around Chrome v56 to preserve resources. Perhaps I've missed a chrome flag that can disable this resource-saving feature so that I can get full webGL performance on a >=4 window application? Otherwise, I'm guessing it's a bug