Add unstable API checks to CI

Author: grovesNL

azure-pipelines.yml

@@ -122,6 +122,10 @@ jobs:
       - script: cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --features Element
       - script: cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --features Window
       - script: cargo test --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --all-features
+      - script: cargo test --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --all-features
+        displayName: "web-sys unstable APIs"
+        env:
+          RUSTFLAGS: --cfg=web_sys_unstable_apis
 
   - job: test_js_sys
     displayName: "Run js-sys crate tests"
@@ -150,6 +154,10 @@ jobs:
       - script: cargo test -p webidl-tests --target wasm32-unknown-unknown
         env:
           WBINDGEN_I_PROMISE_JS_SYNTAX_WORKS_IN_NODE: 1
+      - script: cargo test -p webidl-tests --target wasm32-unknown-unknown
+        displayName: "webidl-tests unstable APIs"
+        env:
+          RUSTFLAGS: --cfg=web_sys_unstable_apis
 
   - job: test_ui
     displayName: "Run UI tests"