Move SkGLContext and some GrGLInterface implementations to skgputest module

src/gpu/gl/SkNullGLContext.cpp

-/*
- * Copyright 2011 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "gl/SkNullGLContext.h"
-#include "gl/GrGLInterface.h"
-
-SkNullGLContext* SkNullGLContext::Create() {
-    SkNullGLContext* ctx = new SkNullGLContext;
-    if (!ctx->isValid()) {
-        delete ctx;
-        return nullptr;
-    }
-    return ctx;
-}
-
-SkNullGLContext::SkNullGLContext() {
-    this->init(GrGLCreateNullInterface());
-}
-
-SkNullGLContext::~SkNullGLContext() {
-    this->teardown();
-}