fetch_end_to_end_test: set env CHROME_HEADLESS=1

This should fix some config hangs such as "fetch android",
which otherwise prompt to accept a Play Services license.

Bug: none
Change-Id: I4e3f59f9541a8e80f04b5b0a48d86e48a19e19bc
Reviewed-on: https://chromium-review.googlesource.com/625876Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>

recipes/recipes/fetch_end_to_end_test.expected/basic.json

@@ -81,6 +81,7 @@
     ],
     "cwd": "[TMP_BASE]/fetch_end_to_end_test_depot_tools_tmp_1",
     "env": {
+      "CHROME_HEADLESS": "1",
       "DEPOT_TOOLS_UPDATE": "0"
     },
     "env_prefixes": {
@@ -101,6 +102,7 @@
       "[TMP_BASE]/fetch_end_to_end_test_depot_tools_tmp_1"
     ],
     "env": {
+      "CHROME_HEADLESS": "1",
       "DEPOT_TOOLS_UPDATE": "0"
     },
     "env_prefixes": {
@@ -120,6 +122,7 @@
     ],
     "cwd": "[TMP_BASE]/fetch_end_to_end_test_infra_tmp_2",
     "env": {
+      "CHROME_HEADLESS": "1",
       "DEPOT_TOOLS_UPDATE": "0"
     },
     "env_prefixes": {
@@ -140,6 +143,7 @@
       "[TMP_BASE]/fetch_end_to_end_test_infra_tmp_2"
     ],
     "env": {
+      "CHROME_HEADLESS": "1",
       "DEPOT_TOOLS_UPDATE": "0"
     },
     "env_prefixes": {

recipes/recipes/fetch_end_to_end_test.py

@@ -27,7 +27,7 @@ def RunSteps(api):
   # Try to run "fetch" for each of the configs. It's important to use
   # the checkout under test.
   with api.context(
-      env={'DEPOT_TOOLS_UPDATE': '0'},
+      env={'DEPOT_TOOLS_UPDATE': '0', 'CHROME_HEADLESS': '1'},
       env_prefixes={'PATH': [api.path['checkout']]}):
     with api.step.defer_results():
       for config_name in fetch_configs: