Remove references on element::Type (m_element_type) in tensor.hpp,types.hpp,convert.hpp (#389)

* remove refs on types in tensor,tensor_view_type,convert

* fix build breaks

src/ngraph/descriptor/tensor.hpp

@@ -17,6 +17,7 @@
 #include <iostream>
 #include <memory>
 #include <vector>
+#include "ngraph/types/type.hpp"
 
 namespace ngraph
 {
@@ -65,7 +66,7 @@ public:
     static std::string make_tensor_name(const Node* node, size_t value_index);
     void set_is_output() { m_is_output = true; }
 protected:
-    const element::Type& m_element_type;
+    const element::Type m_element_type;
     PrimaryTensorView* m_primary_tensor_view;
     bool m_is_output;
     bool m_is_input;

src/ngraph/ops/convert.hpp

@@ -15,6 +15,7 @@
 #pragma once
 
 #include "ngraph/ops/op.hpp"
+#include "ngraph/types/type.hpp"
 
 namespace ngraph
 {
@@ -63,7 +64,7 @@ namespace ngraph
             bool is_functionally_identical(const Node&) const override;
 
         protected:
-            const ngraph::element::Type& m_element_type;
+            const ngraph::element::Type m_element_type;
             virtual void generate_adjoints(autodiff::Adjoints& adjoints,
                                            const std::shared_ptr<Node>& delta) override;
         };

src/ngraph/types/type.hpp

@@ -69,7 +69,7 @@ namespace ngraph
         friend std::ostream& operator<<(std::ostream&, const TensorViewType&);
 
     protected:
-        const element::Type& m_element_type;
+        const element::Type m_element_type;
         Shape m_shape;
     };