Add initial AppVeyor configuration.

.appveyor.yml

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+# Without this "Update next build number or change version format."
+version: "{build}"
+
+environment:
+  global:
+    BAZEL_ROOT: c:\bazel_root\
+    INSTALL_CACHE: c:\install_cache\
+    APPVEYOR_SAVE_CACHE_ON_ERROR: true
+  matrix:
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+
+install:
+  - set PATH=%PATH%;%INSTALL_CACHE%
+  - cmd: tools\appveyor\install.bat
+
+build_script:
+  - cmd: tools\appveyor\build.bat
+
+test_script:
+  - cmd: tools\appveyor\test.bat

tools/appveyor/build.bat

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+REM Copyright 2018, OpenCensus Authors
+REM
+REM Licensed under the Apache License, Version 2.0 (the "License");
+REM you may not use this file except in compliance with the License.
+REM You may obtain a copy of the License at
+REM
+REM     http://www.apache.org/licenses/LICENSE-2.0
+REM
+REM Unless required by applicable law or agreed to in writing, software
+REM distributed under the License is distributed on an "AS IS" BASIS,
+REM WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+REM See the License for the specific language governing permissions and
+REM limitations under the License.
+
+REM TODO: Get everything to build on Windows:
+REM bazel build //...
+
+REM TODO: Remove --output_user_root after https://github.com/bazelbuild/bazel/issues/4149 is fixed.
+bazel --output_user_root=c:/t/ build //opencensus/trace
+
+IF %ERRORLEVEL% NEQ 0 EXIT /b %ERRORLEVEL%
+EXIT /b 0

tools/appveyor/install.bat

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+REM Copyright 2018, OpenCensus Authors
+REM
+REM Licensed under the Apache License, Version 2.0 (the "License");
+REM you may not use this file except in compliance with the License.
+REM You may obtain a copy of the License at
+REM
+REM     http://www.apache.org/licenses/LICENSE-2.0
+REM
+REM Unless required by applicable law or agreed to in writing, software
+REM distributed under the License is distributed on an "AS IS" BASIS,
+REM WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+REM See the License for the specific language governing permissions and
+REM limitations under the License.
+
+REM This script is based on:
+REM https://github.com/google/xrtl/blob/master/tools/ci/appveyor/install.bat
+
+IF NOT EXIST %INSTALL_CACHE% (MKDIR %INSTALL_CACHE%)
+
+REM Download bazel into install cache, which is on the path.
+IF NOT EXIST %INSTALL_CACHE%\bazel.exe (
+  appveyor DownloadFile https://github.com/bazelbuild/bazel/releases/download/0.10.1/bazel-0.10.1-without-jdk-windows-x86_64.exe -FileName %INSTALL_CACHE%\bazel.exe
+)
+
+REM Temporary directory for bazel.
+REM TODO: Remove this after https://github.com/bazelbuild/bazel/issues/4149 is fixed.
+IF NOT EXIST C:\T (MKDIR C:\T)

tools/appveyor/test.bat

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+REM Copyright 2018, OpenCensus Authors
+REM
+REM Licensed under the Apache License, Version 2.0 (the "License");
+REM you may not use this file except in compliance with the License.
+REM You may obtain a copy of the License at
+REM
+REM     http://www.apache.org/licenses/LICENSE-2.0
+REM
+REM Unless required by applicable law or agreed to in writing, software
+REM distributed under the License is distributed on an "AS IS" BASIS,
+REM WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+REM See the License for the specific language governing permissions and
+REM limitations under the License.
+
+REM TODO: Make all tests pass on Windows:
+REM bazel test //...
+
+REM TODO: Remove --output_user_root after https://github.com/bazelbuild/bazel/issues/4149 is fixed.
+REM bazel --output_user_root=c:/t/ test //opencensus/trace:all
+echo TODO: Make all tests pass on Windows.
+
+IF %ERRORLEVEL% NEQ 0 EXIT /b %ERRORLEVEL%
+EXIT /b 0