It turns out that when we were painting the shadows, we painted the them
with the base color once, which contained the alpha, and then blurred it
and used it as a mask for the fill, which has the fill again.
To fix this, always paint the base surface with full alpha. The existing
code applies the blur conditionally sometimes in weird ways, so the code
shuffling fix may not look correct, but be assured it is. If the blur
happens, the new cr we return has the *default* color applied, which is
fully opaque black, which works perfectly against the A8 surface.
The fallback spinner code needs some modification, since it is
intentionally using the alpha to paint the lobes which are "in the past".
Since we shouldn't be hitting this fallback path very often, we use a
temporary group and paint it with paint_with_alpha, even though it is
slow.
Also, in places where we're computing a new CssValue based on an
old one, make sure that if nothing changes we're returning a reference
to the old one, rather than creating a new identical instance.
At the toplevel we have _gtk_theming_engine_get, which lets us pass
in a property context with (atm) the size to get the property for.
Then there is a lot of plumbing to push this down into the lower
layers of the style property code until finally hitting
the property resolvers.
I need this because I will be adding a property resolver for win32
theme parts, and they render differently depending on the size
(i.e. they don't scale linearly). The idea is that the code
to get the background properties will pass in the final size
and we will resolve the theme part specification to that particular
size.
If the old non-context calls are used we just hardcode a size
of 100x100.
