Add output_test.h to output_test_helper for VisualStudio editing.
Add output_test.h to output_test_helper for VisualStudio editing.

efcs/benchmark,codygray/benchmark,mockingbirdnest/benchmark,everbase/benchmark,everbase/benchmark,mockingbirdnest/benchmark,disconnect3d/benchmark,efcs/benchmark,codygray/benchmark,everbase/benchmark,efcs/benchmark,google/benchmark,disconnect3d/benchmark,efcs/benchmark,mockingbirdnest/benchmark,disconnect3d/benchmark,codygray/benchmark,disconnect3d/benchmark,google/benchmark,codygray/benchmark,mockingbirdnest/benchmark,everbase/benchmark,google/benchmark