web-component-tester: Support headless mode

This adds support for running chrome in headless mode.

Support for running firefox in headless mode should work but currently
doesn't.

Moreover, i've added browser option handling to wct [1].

[1] b8388d1a8d

Bug: Issue 8023
Change-Id: I47cd9cd69fc78739219223c74d7b2edf2f97d6c7
(cherry picked from commit f633e0dcac)

polygerrit-ui/app/run_test.sh

@@ -20,5 +20,6 @@ bazel test \
       --test_env="WCT_ARGS=${WCT_ARGS}" \
       --test_env="NPM=${npm_bin}" \
       --test_env="DISPLAY=${DISPLAY}" \
+      --test_env="WCT_HEADLESS_MODE=${WCT_HEADLESS_MODE}" \
       "$@" \
       //polygerrit-ui/app:wct_test

polygerrit-ui/app/wct_test.sh

@@ -12,6 +12,15 @@ unzip -qd $t $code
 mkdir -p $t/test
 cp $TEST_SRCDIR/gerrit/polygerrit-ui/app/test/index.html $t/test/
 
+if [ "${WCT_HEADLESS_MODE:-0}" != "0" ]; then
+    CHROME_OPTIONS=[\'start-maximized\',\'headless\',\'disable-gpu\',\'no-sandbox\']
+    # TODO(paladox): Fix Firefox support for headless mode
+    FIREFOX_OPTIONS=[\'\']
+else
+    CHROME_OPTIONS=[\'start-maximized\']
+    FIREFOX_OPTIONS=[\'\']
+fi
+
 # For some reason wct tries to install selenium into its node_modules
 # directory on first run. If you've installed into /usr/local and
 # aren't running wct as root, you're screwed. Turning this option off
@@ -31,7 +40,11 @@ module.exports = {
       },
       'plugins': {
         'local': {
-          'skipSeleniumInstall': true
+          'skipSeleniumInstall': true,
+          'browserOptions': {
+            'chrome': ${CHROME_OPTIONS},
+            'firefox': ${FIREFOX_OPTIONS}
+          }
         },
         'sauce': {
           'disabled': true,