Adding Google benchmarking library.

third_party/google_benchmark/appveyor.yml

Index: third_party/google_benchmark/appveyor.yml
diff --git a/third_party/google_benchmark/appveyor.yml b/third_party/google_benchmark/appveyor.yml
new file mode 100644
index 0000000000000000000000000000000000000000..e084f386b775cc179bffa1d10c6bd2768cf06cf8
--- /dev/null
+++ b/third_party/google_benchmark/appveyor.yml
@@ -0,0 +1,56 @@
+version: '{build}'
+
+image: Visual Studio 2017
+
+configuration:
+  - Debug
+  - Release
+
+environment:
+  matrix:
+    - compiler: msvc-15-seh
+      generator: "Visual Studio 15 2017"
+
+    - compiler: msvc-15-seh
+      generator: "Visual Studio 15 2017 Win64"
+
+    - compiler: msvc-14-seh
+      generator: "Visual Studio 14 2015"
+
+    - compiler: msvc-14-seh
+      generator: "Visual Studio 14 2015 Win64"
+
+    - compiler: msvc-12-seh
+      generator: "Visual Studio 12 2013"
+
+    - compiler: msvc-12-seh
+      generator: "Visual Studio 12 2013 Win64"
+
+    - compiler: gcc-5.3.0-posix
+      generator: "MinGW Makefiles"
+      cxx_path: 'C:\mingw-w64\i686-5.3.0-posix-dwarf-rt_v4-rev0\mingw32\bin'
+      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+
+matrix:
+  fast_finish: true
+
+install:
+  # git bash conflicts with MinGW makefiles
+  - if "%generator%"=="MinGW Makefiles" (set "PATH=%PATH:C:\Program Files\Git\usr\bin;=%")
+  - if not "%cxx_path%"=="" (set "PATH=%PATH%;%cxx_path%")
+
+build_script:
+  - md _build -Force
+  - cd _build
+  - echo %configuration%
+  - cmake -G "%generator%" "-DCMAKE_BUILD_TYPE=%configuration%" ..
+  - cmake --build . --config %configuration%
+
+test_script:
+  - ctest -c %configuration% --timeout 300 --output-on-failure
+
+artifacts:
+  - path: '_build/CMakeFiles/*.log'
+    name: logs
+  - path: '_build/Testing/**/*.xml'
+    name: test_results