Tests for step parameter of SummaryWriter.(set_)as_default.
Tests for step parameter of SummaryWriter.(set_)as_default.

Four new tests are added:
- we test both constants and variables as step values
- we test as_default and set_as_default methods

For as_default, we also check that the original value is
restored if and only if a non-None step was passed.

davidzchen/tensorflow,tensorflow/tensorflow,cxxgtxy/tensorflow,frreiss/tensorflow-fred,aam-at/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,frreiss/tensorflow-fred,sarvex/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,sarvex/tensorflow,freedomtan/tensorflow,cxxgtxy/tensorflow,davidzchen/tensorflow,davidzchen/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_saved_model,freedomtan/tensorflow,aam-at/tensorflow,annarev/tensorflow,davidzchen/tensorflow,paolodedios/tensorflow,petewarden/tensorflow,aldian/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,annarev/tensorflow,Intel-Corporation/tensorflow,karllessard/tensorflow,cxxgtxy/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,yongtang/tensorflow,yongtang/tensorflow,aldian/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,aam-at/tensorflow,paolodedios/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,karllessard/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,aldian/tensorflow,aam-at/tensorflow,paolodedios/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aldian/tensorflow,sarvex/tensorflow,aam-at/tensorflow,petewarden/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,frreiss/tensorflow-fred,frreiss/tensorflow-fred,yongtang/tensorflow,Intel-tensorflow/tensorflow,petewarden/tensorflow,annarev/tensorflow,paolodedios/tensorflow,sarvex/tensorflow,karllessard/tensorflow,aam-at/tensorflow,tensorflow/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,annarev/tensorflow,yongtang/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorflow-pywrap_saved_model,paolodedios/tensorflow,gautam1858/tensorflow,annarev/tensorflow,aldian/tensorflow,annarev/tensorflow,Intel-tensorflow/tensorflow,petewarden/tensorflow,davidzchen/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,sarvex/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,sarvex/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow,freedomtan/tensorflow,davidzchen/tensorflow,annarev/tensorflow,davidzchen/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,paolodedios/tensorflow,yongtang/tensorflow,aldian/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aldian/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow,cxxgtxy/tensorflow,paolodedios/tensorflow,sarvex/tensorflow,karllessard/tensorflow,freedomtan/tensorflow,davidzchen/tensorflow,annarev/tensorflow,yongtang/tensorflow,aam-at/tensorflow,yongtang/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,frreiss/tensorflow-fred,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,karllessard/tensorflow,aam-at/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,annarev/tensorflow,petewarden/tensorflow,Intel-Corporation/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,tensorflow/tensorflow,frreiss/tensorflow-fred,aldian/tensorflow,frreiss/tensorflow-fred,petewarden/tensorflow,Intel-tensorflow/tensorflow,karllessard/tensorflow,aam-at/tensorflow,frreiss/tensorflow-fred,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,aam-at/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_tf_optimizer,gautam1858/tensorflow,tensorflow/tensorflow,freedomtan/tensorflow,karllessard/tensorflow,petewarden/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,aam-at/tensorflow,freedomtan/tensorflow,frreiss/tensorflow-fred,freedomtan/tensorflow,yongtang/tensorflow,Intel-Corporation/tensorflow,freedomtan/tensorflow,petewarden/tensorflow,Intel-Corporation/tensorflow,paolodedios/tensorflow,Intel-tensorflow/tensorflow,aam-at/tensorflow,davidzchen/tensorflow,freedomtan/tensorflow,Intel-tensorflow/tensorflow,Intel-tensorflow/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,sarvex/tensorflow,davidzchen/tensorflow,cxxgtxy/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_saved_model,annarev/tensorflow,freedomtan/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,Intel-tensorflow/tensorflow,cxxgtxy/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,davidzchen/tensorflow,karllessard/tensorflow,davidzchen/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-Corporation/tensorflow,annarev/tensorflow