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 f633e0dcacd5f6307ef77b3a40d642310e7e60ee)

polygerrit-ui/README.md

@@ -110,6 +110,17 @@ For interactively working on a single test file, do the following:
 
 Then visit http://localhost:8081/elements/foo/bar_test.html
 
+To run Chrome tests in headless mode:
+
+```sh
+WCT_HEADLESS_MODE=1 ./polygerrit-ui/app/run_test.sh
+```
+
+Toolchain requirements for headless mode:
+
+* Chrome: 59+
+* web-component-tester: v6.5.0+
+
 ## Style guide
 
 We follow the [Google JavaScript Style Guide](https://google.github.io/styleguide/javascriptguide.xml)

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,