Move create tensor to mace engine init.

mace/core/mace.cc

@@ -534,7 +534,9 @@ MaceEngine::MaceEngine(const NetDef *net_def, DeviceType device_type) :
     ws_->CreateTensor("mace_input_node:0",
                       GetDeviceAllocator(device_type_),
                       DT_FLOAT);
-
+    ws_->CreateTensor("mace_output_node:0",
+                      GetDeviceAllocator(device_type_),
+                      DT_FLOAT);
     net_ = std::move(CreateNet(op_registry_, *net_def, ws_.get(), device_type));
   }
 }
@@ -551,9 +553,7 @@ bool MaceEngine::Run(const float *input,
                      float *output) {
   MACE_CHECK(output != nullptr, "output ptr cannot be NULL");
   Tensor *input_tensor = ws_->GetTensor("mace_input_node:0");
-  Tensor *output_tensor = ws_->CreateTensor("mace_output_node:0",
-                      GetDeviceAllocator(device_type_),
-                      DT_FLOAT);
+  Tensor *output_tensor = ws_->GetTensor("mace_output_node:0");
   input_tensor->Resize(input_shape);
   {
     Tensor::MappingGuard input_guard(input_tensor);