WebGL compile test (#4966)

ml-agents/tests/yamato/standalone_build_tests.py

 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     parser.add_argument("--scene", default=None)
-    parser.add_argument("--build-target", default="mac", choices=["mac", "linux"])
+    parser.add_argument(
+        "--build-target", default="mac", choices=["mac", "linux", "ios", "webgl"]
+    )
     args = parser.parse_args()
     main(args.scene, args.build_target)

ml-agents/tests/yamato/yamato_utils.py

 import subprocess
 import yaml
 from sys import platform
-from typing import List, Optional
+from typing import List, Optional, Mapping
 
 
 def get_unity_executable_path():
     print(f"Running BuildStandalonePlayer via {unity_exe}")
 
     # enum values from https://docs.unity3d.com/2019.4/Documentation/ScriptReference/BuildTarget.html
-    build_target_to_enum = {
+    build_target_to_enum: Mapping[Optional[str], str] = {
+    # Convert the short name to the official enum
+    # Just pass through if it's not on the list.
+    build_target_enum = build_target_to_enum.get(build_target, build_target)
 
     test_args = [
         unity_exe,
         os.makedirs(os.path.dirname(output_path), exist_ok=True)
     if scene_path is not None:
         test_args += ["--mlagents-build-scene-path", scene_path]
-    if build_target is not None:
-        test_args += ["--mlagents-build-target", build_target_to_enum[build_target]]
+    if build_target_enum is not None:
+        test_args += ["--mlagents-build-target", build_target_enum]
     print(f"{' '.join(test_args)} ...")
 
     timeout = 30 * 60  # 30 minutes, just in case

.yamato/standalone-build-webgl-test.yml

+{% capture editor_version %}2020.2{% endcapture %}
+test_webgl_standalone_{{ editor_version }}:
+  name: Test WebGL Standalone {{ editor_version }}
+  agent:
+    type: Unity::VM
+    image: package-ci/ubuntu:stable
+    flavor: b1.large
+  variables:
+    UNITY_VERSION: {{ editor_version }}
+  commands:
+    - |
+      python3 -m venv venv && source venv/bin/activate
+      python -m pip install pyyaml --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/pypi/simple
+      python -m pip install unity-downloader-cli --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/pypi/simple --upgrade
+      unity-downloader-cli -u {{ editor_version }} -c editor -c WebGL --wait --fast
+      python -u -m ml-agents.tests.yamato.standalone_build_tests --build-target=webgl
+
+  triggers:
+    cancel_old_ci: true
+    recurring:
+      - branch: master
+        frequency: weekly
+  artifacts:
+    logs:
+      paths:
+        - "artifacts/standalone_build.txt"
+    standalonebuild:
+      paths:
+        - "artifacts/testPlayer*/**"
+        - "artifacts/**/UnityPlayer.so"