Refactor GL bindings so there is no global GLApi or DriverGL.

gpu/ipc/service/image_transport_surface_mac.mm

Index: gpu/ipc/service/image_transport_surface_mac.mm
diff --git a/gpu/ipc/service/image_transport_surface_mac.mm b/gpu/ipc/service/image_transport_surface_mac.mm
index 2d306748ad634e9550ed07bdd5a51978c2f64a15..2dd88d5a9c7547e77c2cb2907166213a1a338e83 100644
--- a/gpu/ipc/service/image_transport_surface_mac.mm
+++ b/gpu/ipc/service/image_transport_surface_mac.mm
@@ -55,6 +55,7 @@ scoped_refptr<gl::GLSurface> ImageTransportSurface::CreateNativeSurface(
       return make_scoped_refptr<gl::GLSurface>(
           new ImageTransportSurfaceOverlayMac(delegate));
     case gl::kGLImplementationMockGL:
+    case gl::kGLImplementationStubGL:
       return make_scoped_refptr<gl::GLSurface>(new gl::GLSurfaceStub);
     default:
       // Content shell in DRT mode spins up a gpu process which needs an