Merge pull request #12944 from dbudniko:dbudniko/tests_thresholds

* added threshold to g-api imgproc tests

* trailing spaces remove

* try to fix warnings

* fix license header

* fix random numbers issue

* fix Sobel test

* license headers + precompiled headers included

modules/gapi/perf/common/gapi_imgproc_perf_tests.cpp

@@ -0,0 +1,9 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+//
+// Copyright (C) 2018 Intel Corporation
+
+
+#include "perf_precomp.hpp"
+#include "gapi_imgproc_perf_tests_inl.hpp"