Use of dGPU on Chromium 60+
I apologize, but I am now back with another issue! Just like last time, this one is also a Chromium issue, rather than a Vivaldi specific one.
While testing the 1.11 snapshots of Vivaldi that ride on top of Chromium 60, I noticed that macOS would switch from my iGPU to the dGPU every time I launched the browser. The dependency process was always the main browser process, rather than a specific tab, so nothing could be done. I tested Chromium 60 and Google Chrome Canary 62 and both had the same issue. It seems as if the Chromium developers made some change with 60 that is causing this, as Chromium 59 and lower were fine.
The iGPU on my MacBook pro is the Intel HD Graphics 3000 and the dGPU is an AMD Radeon HD 9450M (and I am on macOS Sierra 10.12.6). Needless to say, battery life with the dGPU on 100% of the time is terrible, so I have been running gfxCardStatus to disable the dGPU all of the time now. (Both of the GPU's in this laptop have been an absolute PITA and I am looking at replacing it with a new MBP.)
I know there is nothing that can be done here, but I figured I would just give everyone else with one of these problematic 15" 2011 MacBook Pro's a heads up!
Please report bug to https://bugs.chromium.org/p/chromium/issues/list.
If Chromium devs fix it, Vivaldi devs can fix it after they get the new code.
It appears, that you've found the root cause of what is discussed for a couple of years here: