Sorry for my English, I am french.
Thanks you for the method to reproduce, I tested and i can do it. I tested three times 😀
Since the update to Yosemite, I have the same problem that you. So today, I decide to check logs to find the source of problem.
After some minutes, I arrived here.
I installed gfxCardStatus to check the switching during Safari browsing (wonderful application).
So i can see on what page the GPU switch and I surfing until at http://amazon-operations.fr/nos-métiers
The GPU switched, any freeze the first time... (second time it did...) OK...
For this moment, I don't disable the switching in settings OS X, in my mind, disable a setting on the global system, just for one application, it's not possible....
The bug is in Safari and not elsewhere...
So, I am thinking and say to me that only on Safari, why Safari ask the switching of GPU on this page.
I go in Safari Preferences to find a setting which could change that.
Oh, there is Enable WebGL. I always let enabled. And GL is Graphic Library 😀
If I disable it, maybe... It's DONE
I refresh the same page, and oh, and GPU is not switched. It's same for the test page posted.
So guys, what do you think ? Can you test to disable and post your feedback ?