GPU: Keep track of the last real context and real surface made current.

ui/gl/gl_surface_osmesa.cc

Index: ui/gl/gl_surface_osmesa.cc
diff --git a/ui/gl/gl_surface_osmesa.cc b/ui/gl/gl_surface_osmesa.cc
index 7994eec379187df5b0838ab1f7749615d8fff3ae..980b28f0b019323165a20ba19e0f3f5bcbb7e8ac 100644
--- a/ui/gl/gl_surface_osmesa.cc
+++ b/ui/gl/gl_surface_osmesa.cc
@@ -23,7 +23,7 @@ void GLSurfaceOSMesa::Destroy() {
 }
 
 bool GLSurfaceOSMesa::Resize(const gfx::Size& new_size) {
-  GLContext* current_context = GLContext::GetCurrent();
+  GLContext* current_context = GLContext::GetRealCurrent();

[no sievers, 2013/05/24 21:48:06]

Wait, why does this have to get the real context here then?
And isn't that a problem if a virtual context was current, that we will now
return from here with the real context being set current for both
GLContext::GetCurrent() and GLContext::GetRealCurrent()?

Is this just to keep the virtual API from potentially skipping the context
switch below in line 52? Would it?

[jonathan.backer, 2013/05/27 16:37:36]

AFAICT, this code it about resizing a buffer that may be in use. If it's in use,
we need to release, resize, rebind.

In practice, this surface could be current with a real context or a virtual
context. But it's the real binding that matters (not the virtual binding). Note,
a surface being current virtually does not always mean that it's current for
real (there's a 'lite' path in VirtualGLApi::MakeCurrent).
Yes. This is a problem. Thank you. I'm going to fix this with a
ScopedMakeCurrent.
No. The reset in line 52 is a bug (I should restore whatever was previously
current --- including virtual contexts).

   bool was_current = current_context && current_context->IsCurrent(this);
   if (was_current)
     current_context->ReleaseCurrent(this);