* Upgrade gtest for clang-tidy. * Use CMake to install GTest instead of mv. * Don't enforce clang-tidy to return 0 due to errors in thrust. * Add a small test for tidy itself. * Reformat.
* Add PushCSC for SparsePage. * Move Push* definitions into cc file. * Add std:: prefix to `size_t` make clang++ happy. * Address monitor count == 0.