I have read all - and on the bottom i found this:
Thanks for the feedback.
When I ran your app, I got about 30 FPS full-screen. To see if I could reproduce it in my own setup, I modified the latest GDI Sample (which uses kWebViewType_Windowed), enabled WebGL and GPU acceleration, and set the GL Mode to Desktop. When I ran it full-screen I got 60 FPS
(which is the maximum with vsync) with lower CPU usage.
So, there must be some difference in your code.
I've attached my modifications to the GDI Sample below, try building it and comparing it with your code.