Add a basic custom painting facility to Sky

Add a basic custom painting facility to Sky

This CL adds just enough custom painting to Sky to make
sky/examples/painting/circle.sky draw a circle. Over time, we should be able to
elaborate this system into something interesting and to make it actually work
in a reasonable way.

R=ojan@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/060a6ba51889aad8b4bc400dd7503cf0415b4677

[ojan, 2015-03-19 22:30:04]

lgtm. I just left some comments for things I noticed as I was reviewing of
followup steps.

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/dom/Ele...
File sky/engine/core/dom/Element.cpp (right):

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/dom/Ele...
sky/engine/core/dom/Element.cpp:425: element->document().updateLayout();
We should not need to do this. I guess that falls out from scheduling the work
at a more reasonable time? We'll need to figure out how to get these callbacks
to not be able to change the tree structure.

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/paintin...
File sky/engine/core/painting/Paint.h (right):

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/paintin...
sky/engine/core/painting/Paint.h:32: m_paint.setARGB(a, r, g, b);
hah

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/renderi...
File sky/engine/core/rendering/RenderBox.cpp (right):

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/renderi...
sky/engine/core/rendering/RenderBox.cpp:992: // TODO(abarth): Currently we only
draw m_customPainting if we happen to
I think we want to do this before we do any other painting. I think in the final
result we'll probably want 3 different callbacks. beforePaint, paint and
afterPaint.

beforePaint: happens before the default paint (including backgrounds, etc.
paint: the default paint. if you set this callback then we skip the default
paint code.
afterPaint: happens after paint. :)

We can fix this in followup patches of course.

[abarth-chromium, 2015-03-19 22:34:27]

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/renderi...
File sky/engine/core/rendering/RenderBox.cpp (right):

https://codereview.chromium.org/1017593005/diff/20001/sky/engine/core/renderi...
sky/engine/core/rendering/RenderBox.cpp:992: // TODO(abarth): Currently we only
draw m_customPainting if we happen to
On 2015/03/19 at 22:30:04, ojan wrote:
> I think we want to do this before we do any other painting. I think in the
final result we'll probably want 3 different callbacks. beforePaint, paint and
afterPaint.
> 
> beforePaint: happens before the default paint (including backgrounds, etc.
> paint: the default paint. if you set this callback then we skip the default
paint code.
> afterPaint: happens after paint. :)
> 
> We can fix this in followup patches of course.

Yeah, the main design question is whether these paint callbacks should be
synchronous.  One idea is to make them asynchronous (as implemented in this CL),
and basically generate SkPictures that get played back at these times.  The
script is then responsible for invalidating the SkPictures as appropriate. 
Presumably we'll want to make it easy to invalidate your picture when the size
of your box changes.

[abarth-chromium, 2015-03-19 23:00:25]

Committed patchset #2 (id:20001) manually as
060a6ba51889aad8b4bc400dd7503cf0415b4677 (presubmit successful).