Messages in other ones come regularly in capabilities autodetection (the only way how to find out rendering into which render target formats is supported is to do trial frame buffer creation and check for status, which also triggers built-in warnings).
But even this one could be bogus, I already noticed out-of-order logging into console before, so even this "framebuffer incomplete" error can be still part of the autodetection.
At this point I do not know, something is not behaving as it should be on these Intel GPUs, though curiously it does work ok on my older Intel HD 3000 under Windows 7.
If you can (on Windows), you can try to enable DX11 ANGLE rendering backend in Chrome and see it it makes any difference (more capabilities are available with DX11, I use different code paths when more advanced features are present).
It's available via chrome://flags/ under "Enable D3D11" and should work in current stable Chrome 33 (though in Chrome Canary 35 it does work better).
