Ensure that the serial device is enabled during part of OrientNormals test.

Once #377 is implemented we won't need this, but for now we have to
use the serial connectivity tables while validating the OrientNormals
output. Ensure that the serial device can be used during the validation
stage.

vtkm/worklet/testing/UnitTestOrientNormals.cxx

@@ -43,6 +43,7 @@
 
 #include <vtkm/cont/testing/Testing.h>
 
+#include <vtkm/cont/RuntimeDeviceTracker.h>
 
 namespace
 {
@@ -128,6 +129,12 @@ struct ValidateNormals
                   bool checkCells,
                   const std::string& normalsName = "normals")
   {
+    // Temporarily enable the serial device for workaround in ValidateNormals,
+    // which requires the serial device. This can be refactored once #377 is
+    // fixed.
+    vtkm::cont::ScopedRuntimeDeviceTracker tracker(vtkm::cont::DeviceAdapterTagSerial{},
+                                                   vtkm::cont::RuntimeDeviceTrackerMode::Enable);
+
     vtkm::cont::Field pointNormals;
     vtkm::cont::Field cellNormals;
 
@@ -157,7 +164,7 @@ struct ValidateNormals
     , CheckCells(checkCells)
   {
     // FIXME This would be much simplier if we had a GetPointCells() method on
-    // cell sets....
+    // cell sets.... #377 will simplify this.
     // Build the connectivity table on any device, then get a portal for serial
     // so we can do lookups on the CPU.
     this->Cells.GetConnectivityArray(vtkm::TopologyElementTagCell{},