Enable Web Components V0 APIs for perf youtube test.

This patch is a preparation for Shadow DOM V0, Custom Element V0 (CEv0) and HTML Imports removal.
Intent to Deprecate and Remove: http://bit.ly/2RGHe3x
Though we soon make these APIs only available for test by turning the json5 feature flag
from status: "stable" to status: "test" (crrev.com/c/1399776), there is browser tests/chrome internal components that
use them.

This patch keeps perf tests loading YouTube use the V0 APIs regardless of the json5 runtime flag
When YouTube finishes migration to V1 APIs, we can remove this temporary flag.

Bug: 911943
TEST: python ../../tools/perf/run_tests --jobs=1 --test-filter=benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/browse:media:youtube:2018::benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/browse_accessibility:media:youtube
Change-Id: I6f93b803aa64a813321dc6476cc13e79ab3e1f34
Reviewed-on: https://chromium-review.googlesource.com/c/1414391
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623486}
2 files changed