Turn on proto trace generation on android-nexus5x-perf-fyi bot

Before we turn proto trace generation on for all bots, we want to make
sure that it works on Android.

Bug: 1028612
Change-Id: Ie013950818a1d6de0181e474387c0dc6a7c8eb81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980574Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Mikhail Khokhlov <khokhlov@google.com>
Cr-Commit-Position: refs/heads/master@{#727269}

testing/buildbot/chromium.perf.fyi.json

@@ -9,7 +9,8 @@
           "--browser=android-chrome",
           "--upload-results",
           "--test-shard-map-filename=android-nexus5x-perf-fyi_map.json",
-          "--output-format=histograms"
+          "--output-format=histograms",
+          "--experimental-proto-trace-format"
         ],
         "isolate_name": "performance_test_suite",
         "merge": {

tools/perf/core/perf_data_generator.py

@@ -98,6 +98,7 @@ FYI_BUILDERS = {
         'isolate': 'performance_test_suite',
         'extra_args': [
           '--output-format=histograms',
+          '--experimental-proto-trace-format',
         ],
       }
     ],