Add --passthrough command line arg for Telemetry-based GPU tests.

content/test/gpu/generate_buildbot_json.py

Index: content/test/gpu/generate_buildbot_json.py
diff --git a/content/test/gpu/generate_buildbot_json.py b/content/test/gpu/generate_buildbot_json.py
index f32b73f791a257f6a0fcf0524b102af533afaab5..57fde945f83ef0d203bb86f33b9ac76587640a69 100755
--- a/content/test/gpu/generate_buildbot_json.py
+++ b/content/test/gpu/generate_buildbot_json.py
@@ -2305,7 +2305,11 @@ def generate_telemetry_test(tester_name, tester_config,
   prefix_args = [
     benchmark_name,
     '--show-stdout',
-    '--browser=%s' % tester_config['build_config'].lower()
+    '--browser=%s' % tester_config['build_config'].lower(),
+    # --passthrough displays more of the logging in Telemetry when run
+    # --via typ, in particular some of the warnings about tests being
+    # --expected to fail, but passing.
+    '--passthrough',
   ]
   return generate_isolated_test(tester_name, tester_config, test,
                                 test_config, extra_browser_args,