created perf test for DFT

modules/core/perf/perf_dft.cpp

+#include "perf_precomp.hpp"
+
+using namespace std;
+using namespace cv;
+using namespace perf;
+
+#define MAT_TYPES_DFT  CV_32FC1, CV_64FC1
+#define MAT_SIZES_DFT  sz1080p, sz2K
+#define TEST_MATS_DFT testing::Combine( testing::Values(MAT_SIZES_DFT), testing::Values(MAT_TYPES_DFT) )
+
+PERF_TEST_P(Size_MatType, dft, TEST_MATS_DFT)
+{
+    Size sz = std::tr1::get<0>(GetParam());
+    int type = std::tr1::get<1>(GetParam());
+
+    Mat src(sz, type);
+    Mat dst(sz, type);
+ 
+    declare.in(src, WARMUP_RNG);
+    declare.time(60);
+
+    TEST_CYCLE(100) 
+	{ 
+        dft(src, dst, 0.f);
+	}
+
+    SANITY_CHECK(dst);
+}