Implement GLX for Ozone X11.

ui/gl/gl_context_ozone.cc

Index: ui/gl/gl_context_ozone.cc
diff --git a/ui/gl/gl_context_ozone.cc b/ui/gl/gl_context_ozone.cc
index d62b5686b9ed63b0ac5e5a18984dafc0326e905a..2b34585c6b409cf8337fcbb42051286210659863 100644
--- a/ui/gl/gl_context_ozone.cc
+++ b/ui/gl/gl_context_ozone.cc
@@ -14,6 +14,10 @@
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 
+#if defined(USE_GLX)
+#include "ui/gl/gl_context_glx.h"
+#endif
+
 namespace gfx {
 
 // static
@@ -25,6 +29,14 @@ scoped_refptr<GLContext> GLContext::CreateGLContext(
   switch (GetGLImplementation()) {
     case kGLImplementationMockGL:
       return scoped_refptr<GLContext>(new GLContextStub());
+#if defined(USE_GLX)

[rjkroege, 2016/04/27 19:08:12]

The #ifdef and configuration is unfortunate as it breaks the promise of the
ozone platform abstraction. In an ideal world, adding or removing an ozone
platform (e.g. ozone x11) shouldn't require recompiling any code from ui/gl. 

One of our goals is to eventually make Linux Chrome Ozone run identically on
desktop and chrome books with the only difference being which ozone platforms
have been compiled. So, is it possible to restructure this so that the context
creation is pushed into the platform implementation?

[kylechar, 2016/04/27 19:36:32]

So, it's definitely possible with one very large refactor. Right now //ui/gl has
a dep of //ui/ozone. That means ozone can't create the GLContext/GLSurface.
spang@ had the idea to split //ui/gl into //ui/gl + //ui/gl:gl_base. The
GLContext/GLSurfaces go into //ui/gl:gl_base, then //ui/ozone depends on
//ui/gl:gl_base and finally //ui/gl depends on //ui/ozone. The static methods to
create a new GLContext/GLSurface are in //ui/gl which can then delegate it to
the Ozone platform.

I started the refactor to see how feasible it will be. It's going to modify a
couple hundred files and make some big changes to how //ui/gl is structured, so
I'm weary to continue without buy in.

+    case kGLImplementationDesktopGL: {
+      scoped_refptr<GLContext> context(new GLContextGLX(share_group));
+      if (!context->Initialize(compatible_surface, gpu_preference))
+        return nullptr;
+      return context;
+    }
+#endif
     case kGLImplementationOSMesaGL: {
       scoped_refptr<GLContext> context(new GLContextOSMesa(share_group));
       if (!context->Initialize(compatible_surface, gpu_preference))