Add base class for GLTestContext and add new subclass VkTestContext.

tools/gpu/vk/VkTestContext.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "VkTestContext.h"
+
+#ifdef SK_VULKAN
+
+namespace {
+// TODO: Implement fence syncs and swap buffers
+class VkTestContextImpl : public sk_gpu_test::VkTestContext {
+public:
+    VkTestContextImpl()
+        : VkTestContext(sk_sp<const GrVkBackendContext>(GrVkBackendContext::Create())) {}
+
+    ~VkTestContextImpl() override { this->teardown(); }
+
+    void testAbandon() override {}
+
+protected:
+    void teardown() override { fVk.reset(nullptr); }
+
+private:
+    void onPlatformMakeCurrent() const override {}
+    void onPlatformSwapBuffers() const override {}
+
+    typedef sk_gpu_test::VkTestContext INHERITED;
+};
+}
+
+namespace sk_gpu_test {
+VkTestContext* CreatePlatformVkTestContext() {
+    return new VkTestContextImpl;
+}
+}  // namespace sk_gpu_test
+
+#endif