Assigning to Petr for triage, since it's a fuchsia upstream builder and this is causing, cc'ing a few people who may care.

Context:
- Try job for Fuchsia on Chromium
- A unit test is flaky, in this case WebContentsImplTest.UseTitleFromPendingEntryIfSet (I haven't filed a bug for this)
- The recipe tries to retry the test case, without test_launcher retries.
- The Fuchsia unit test doesn't use test_launcher

Expected:
- The recipe knows that it's running for fuchsia, and use the right flag

Actual:
- The retries are worthless, causing the whole recipe run to be unconditionally rerun.


Tak:
https://chromium-swarm.appspot.com/task?id=41771f3ce5f23b10

Command:
bin/run_content_unittests --test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.content_unittests.filter --qemu-require-kvm --gtest_repeat=10 --test-launcher-retry-limit=0 --gtest_filter=WebContentsImplTest.UseTitleFromPendingEntryIfSet --test-launcher-summary-output=/b/s/w/ioBiLg0n/output.json

Result:
test_runner.py: error: unrecognized arguments: --test-launcher-retry-limit=0

From build:
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/fuchsia_x64/160021

From CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1354754