Add support for EGL on linux

src/gpu/gl/unix/GrGLCreateNativeInterface_unix.cpp

-/*
- * Copyright 2014 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-
-#include "gl/GrGLInterface.h"
-#include "gl/GrGLAssembleInterface.h"
-#include "gl/GrGLUtil.h"
-
-#include <GL/glx.h>
-
-static GrGLFuncPtr glx_get(void* ctx, const char name[]) {
-    SkASSERT(NULL == ctx);
-    SkASSERT(glXGetCurrentContext());
-    return glXGetProcAddress(reinterpret_cast<const GLubyte*>(name));
-}
-
-const GrGLInterface* GrGLCreateNativeInterface() {
-    if (NULL == glXGetCurrentContext()) {
-        return NULL;
-    }
-
-    return GrGLAssembleInterface(NULL, glx_get);
-}