shiny/widget/node: rename some function args.

FooEmbed receivers go from e to m. Event args go from ev to e.

Using e for events is consistent with other shiny code, such as
widget.go.

Change-Id: I4a33534616514ee8086896aff79d7c9a9c79a99d
Reviewed-on: https://go-review.googlesource.com/23075
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
2 files changed