Move GPU fences into sk_gpu_test

tools/gpu/FenceSync.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef FenceSync_DEFINED
+#define FenceSync_DEFINED
+
+#include "SkTypes.h"
+
+namespace sk_gpu_test {
+
+using PlatformFence = intptr_t;
+static constexpr PlatformFence kInvalidPlatformFence = 0;
+
+/*
+ * This class provides an interface to interact with fence syncs. A fence sync is an object that the
+ * client can insert into the GPU command stream, and then at any future time, wait until all
+ * commands that were issued before the fence have completed.
+ */
+class FenceSync {
+public:
+    virtual PlatformFence SK_WARN_UNUSED_RESULT insertFence() const = 0;
+    virtual bool waitFence(PlatformFence) const = 0;
+    virtual void deleteFence(PlatformFence) const = 0;
+
+    virtual ~FenceSync() {}
+};
+
+}
+
+#endif