Tests: Download Chromium for e2e tests only.

This reduces the chance of random failures due to network timeouts and avoids the overhead of unnecessarily downloading ~120 MB for PHP or JS tests.

Fixes #49621.

git-svn-id: https://develop.svn.wordpress.org/trunk@47449 602fd350-edb4-49c9-b593-d223f7449a82

.travis.yml

@@ -74,6 +74,10 @@ before_script:
 - npm --version
 - node --version
 - nvm install 10.13.0
+- |
+  if [[ "$WP_TRAVISCI" != "test:e2e" ]]; then
+    npm config set puppeteer_skip_chromium_download true
+  fi
 - |
   if [[ "$NPM_INSTALL" == "true" ]]; then
     npm ci