Merge pull request #15419 from OrestChura:gapi_headers_internal_flag_issue

* - headers in "infer/" and "infer/ie/" folders are included into gapi_ext_hdrs;
+ because of that a few #includes are required in the headers
- HAVE_INF_ENGINE flag check in headers "infer/ie.hpp" and "infer/ie/util.hpp" is deleted

* - the "ie/util.hpp" header is a private header now as it's used for tests; it's been moved to the scr directory to the place next to the implementation file "ie/giebackend.cpp"
- the path to this header in files "ie/giebackend.cpp" and "test/infer/gapi_infer_ie_test.cpp" is updated
- As it's private header now and explicitly depends on IE, the "HAVE_INF_ENGINE" flag check is returned

modules/gapi/src/backends/ie/giebackend.cpp

@@ -28,12 +28,12 @@
 #include <opencv2/gapi/gtype_traits.hpp>
 
 #include <opencv2/gapi/infer.hpp>
-#include <opencv2/gapi/infer/ie/util.hpp>
 
 #include "compiler/gobjref.hpp"
 #include "compiler/gmodel.hpp"
 
 #include "backends/ie/giebackend.hpp"
+#include "backends/ie/util.hpp"
 
 #include "api/gbackend_priv.hpp" // FIXME: Make it part of Backend SDK!
 

modules/gapi/src/backends/ie/util.hpp

@@ -0,0 +1,35 @@
+// 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) 2019 Intel Corporation
+
+#ifndef OPENCV_GAPI_INFER_IE_UTIL_HPP
+#define OPENCV_GAPI_INFER_IE_UTIL_HPP
+
+#ifdef HAVE_INF_ENGINE
+
+// NOTE: This file is not included by default in infer/ie.hpp
+// and won't be. infer/ie.hpp doesn't depend on IE headers itself.
+// This file does -- so needs to be included separately by those who care.
+
+#include "inference_engine.hpp"
+
+#include <opencv2/core/cvdef.h>     // GAPI_EXPORTS
+#include <opencv2/gapi/gkernel.hpp> // GKernelPackage
+
+namespace cv {
+namespace gapi {
+namespace ie {
+namespace util {
+
+GAPI_EXPORTS std::vector<int> to_ocv(const InferenceEngine::SizeVector &dims);
+
+GAPI_EXPORTS cv::Mat to_ocv(InferenceEngine::Blob::Ptr blob);
+GAPI_EXPORTS InferenceEngine::Blob::Ptr to_ie(cv::Mat &blob);
+
+}}}}
+
+#endif //HAVE_INF_ENGINE
+
+#endif // OPENCV_GAPI_INFER_IE_UTIL_HPP