Make GL calls go through subclassable class.

ui/gl/gl_implementation.cc

Index: ui/gl/gl_implementation.cc
diff --git a/ui/gl/gl_implementation.cc b/ui/gl/gl_implementation.cc
index 0a10f224fce682138d50249b68425114b5db0322..a97a4df558a7983d46402fb822cb5faa478a7935 100644
--- a/ui/gl/gl_implementation.cc
+++ b/ui/gl/gl_implementation.cc
@@ -10,6 +10,7 @@
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "ui/gl/gl_bindings.h"
 
 namespace gfx {
 
@@ -62,6 +63,25 @@ bool ExportsCoreFunctionsFromGetProcAddress(GLImplementation implementation) {
 
 }
 
+GLApi* g_current_gl_context;
+OSMESAApi* g_current_osmesa_context;
+
+#if defined(OS_WIN)
+
+EGLApi* g_current_egl_context;
+WGLApi* g_current_wgl_context;
+
+#elif defined(USE_X11)
+
+EGLApi* g_current_egl_context;
+GLXApi* g_current_glx_context;
+
+#elif defined(OS_ANDROID)
+
+EGLApi* g_current_egl_context;
+
+#endif
+
 GLImplementation GetNamedGLImplementation(const std::string& name) {
   for (size_t i = 0; i < ARRAYSIZE_UNSAFE(kGLImplementationNamePairs); ++i) {
     if (name == kGLImplementationNamePairs[i].name)