Make GL calls go through subclassable class.

ui/gl/gl_bindings.h

Index: ui/gl/gl_bindings.h
diff --git a/ui/gl/gl_bindings.h b/ui/gl/gl_bindings.h
index 4999e8dc45fe116c8f572579f2ca0b3a60a8f3e1..adf956b876e09c46dac30f3bb5eb15b434258641 100644
--- a/ui/gl/gl_bindings.h
+++ b/ui/gl/gl_bindings.h
@@ -96,6 +96,32 @@ typedef Window   EGLNativeWindowType;
 
 namespace gfx {
 
+GL_EXPORT extern GLApi* g_current_gl_context;
+GL_EXPORT extern OSMESAApi* g_current_osmesa_context;
+GL_EXPORT extern DriverGL g_driver_gl;
+GL_EXPORT extern DriverOSMESA g_driver_osmesa;
+
+#if defined(OS_WIN)
+
+GL_EXPORT extern EGLApi* g_current_egl_context;
+GL_EXPORT extern WGLApi* g_current_wgl_context;
+GL_EXPORT extern DriverEGL g_driver_egl;
+GL_EXPORT extern DriverWGL g_driver_wgl;
+
+#elif defined(USE_X11)
+
+GL_EXPORT extern EGLApi* g_current_egl_context;
+GL_EXPORT extern GLXApi* g_current_glx_context;
+GL_EXPORT extern DriverEGL g_driver_egl;
+GL_EXPORT extern DriverGLX g_driver_glx;
+
+#elif defined(OS_ANDROID)
+
+GL_EXPORT extern EGLApi* g_current_egl_context;
+GL_EXPORT extern DriverEGL g_driver_egl;
+
+#endif
+
 // Find an entry point to the mock GL implementation.
 void* GL_BINDING_CALL GetMockGLProcAddress(const char* name);