[WIP] Implement BackGroundFilter as seperate layer in cc

Currently background filters just allow you to apply a
FilterOperation to some content in a frame by doing a copy
into a texture and applying the FilterOperations there.

But there are many things than cc layers can do (eg.
clipping/transforms) that FilterOperations couldn't. So now
people keep having to write new shaders in Skia and new
FilterOperations to do these types of things such as
zooming.

If instead a background filter was a Layer type that simply
copies whatever is already in its target at some bounding
box (doesn't need to be its own position/size), and then
produces that copied stuff as its own output again wherever
it is positioned. Then it could just use foreground filters
to apply effects, as well as transform etc.

BUG=392214

[Sikugu_, 2015-03-05 13:00:10]

sivagunturi@chromium.org changed reviewers:
- danakj@chromium.org