Allow Scrolling

[TotallyGamerJet]

I think it would be cool if you could scroll with a mouse instead of having to drag! That's all, great project.

[pchampio]

The flutter engine does not support scrolling through the Scrollwheel at the moment.
They are working on it: flutter/engine#6228

[GeertJohan]

Enum and field in embedder.h support suggest support for scrolling.

https://github.com/flutter/engine/blob/4b01d795feec3ba8231a397a4ec2759954d8216e/shell/platform/embedder/embedder.h#L292
and
https://github.com/flutter/engine/blob/4b01d795feec3ba8231a397a4ec2759954d8216e/shell/platform/embedder/embedder.h#L307

GLFW hook would be https://godoc.org/github.com/go-gl/glfw/v3.2/glfw#ScrollCallback

[GeertJohan]

Unpinned, on hold until the embedder support lands in beta channel.

[GeertJohan]

Support for scrolling has just been merged to master as a633350