Enable the Sky compositor again

Enable the Sky compositor again

This CL fixes two bugs:

1) We need to enter the Ganesh context in order to destroy the GrContext.

2) We had a race condition whereby we'd try to upload a frame to a surface that
   didn't yet exist. This CL fixes that race by adding a state to LayerHost to
   wait for the surface to be created before trying to upload to it.

R=esprehn@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/09751e2b44f5e94c93c7020f7867bdf88b76105e

[abarth-chromium, 2014-11-21 19:32:04]

abarth@chromium.org changed reviewers:
+ esprehn@chromium.org, ojan@chromium.org, rafaelw@chromium.org

[esprehn, 2014-11-21 19:34:45]

https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc
File sky/compositor/layer_host.cc (right):

https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc...
sky/compositor/layer_host.cc:74: if (state_ == kProducingFrame)
What schedules the eventual upload if it wasn't ready on the first try?

[abarth-chromium, 2014-11-21 20:01:17]

https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc
File sky/compositor/layer_host.cc (right):

https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc...
sky/compositor/layer_host.cc:74: if (state_ == kProducingFrame)
On 2014/11/21 at 19:34:45, esprehn wrote:
> What schedules the eventual upload if it wasn't ready on the first try?

The OnSurfaceIdAvailable callback is called whenever we attach to a surface.  If
we haven't attached to a surface yet, we just want until the next
OnSurfaceIdAvailable callback.  I can add a comment explaining that if you like.

[esprehn, 2014-11-21 20:03:19]

On 2014/11/21 at 20:01:17, abarth wrote:
> https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc
> File sky/compositor/layer_host.cc (right):
> 
>
https://codereview.chromium.org/753643002/diff/1/sky/compositor/layer_host.cc...
> sky/compositor/layer_host.cc:74: if (state_ == kProducingFrame)
> On 2014/11/21 at 19:34:45, esprehn wrote:
> > What schedules the eventual upload if it wasn't ready on the first try?
> 
> The OnSurfaceIdAvailable callback is called whenever we attach to a surface. 
If we haven't attached to a surface yet, we just want until the next
OnSurfaceIdAvailable callback.  I can add a comment explaining that if you like.

Will we block doing another BeginFrame until the surface is available?

lgtm

[abarth-chromium, 2014-11-21 20:07:27]

On 2014/11/21 at 20:03:19, esprehn wrote:
> Will we block doing another BeginFrame until the surface is available?

No, we'll keep scheduling frames while we're in this state.

This is tied up in the fact that we're using a timer to drive BeginFrame rather
than feedback from the graphics pipeline.  I have a local branch where we use
feedback from the graphics pipeline to drive BeginFrame.  In that branch, we
don't even get into BeginFrame until we've attached to a surface.  However, we
need to fix some things in the surfaces system before we can use that approach.

[abarth-chromium, 2014-11-21 20:08:37]

The timer-based approach matches the behavior we're currently getting from CC,
which is why I went with that approach on trunk for the time being.

[abarth-chromium, 2014-11-21 20:15:35]

Committed patchset #2 (id:20001) manually as
09751e2b44f5e94c93c7020f7867bdf88b76105e (presubmit successful).