Tests/LibWeb: Add a flag to update expectation metadata in WPT runner

Adds `--update-expectations-metadata` that allows to automatically
rebuild metadata.txt file with test expectations.

Tests/LibWeb/WPT/run.sh

@@ -7,6 +7,12 @@ then
     echo "SERENITY_SOURCE_DIR is not set. Exiting."
 fi
 
+if [[ "$1" == "--update-expectations-metadata" ]]; then
+    update_expectations_metadata=true
+else
+    update_expectations_metadata=false
+fi
+
 # NOTE: WPT runner assumes Ladybird, WebContent and WebDriver are available in $PATH.
 export PATH="${SERENITY_SOURCE_DIR}/Build/lagom/bin:${SERENITY_SOURCE_DIR}/Meta/Lagom/Build/bin:${PATH}"
 
@@ -31,5 +37,14 @@ git clone --depth 10000 https://github.com/web-platform-tests/wpt.git
 # Extract metadata.txt into directory with expectation files expected by WPT runner
 ./concat-extract-metadata.py --extract metadata.txt metadata
 
+# Generate name for file with wpt run log
+wpt_run_log_filename="$(mktemp).txt"
+
 # Run tests.
 ./wpt/wpt run ladybird --no-fail-on-unexpected --no-fail-on-unexpected-pass --skip-timeout --include-manifest include.ini --metadata ./metadata --manifest ./MANIFEST.json --log-raw "${wpt_run_log_filename}"
+
+# Update expectations metadata files if requested
+if [[ $update_expectations_metadata == true ]]; then
+    ./wpt/wpt update-expectations --product ladybird --metadata ./metadata --manifest ./MANIFEST.json "${wpt_run_log_filename}"
+    ./concat-extract-metadata.py --concat ./metadata > metadata.txt
+fi