[networking_private] Add TrafficCounterResetTime to idl

Add |TrafficCounterResetTime| to webidl to prevent client side error
'Unexpected Property'.

Bug: b:331214001, b:333397479, b:40208225
Test: 'autoninja -C out/Default/ chrome/test:browser_tests && xvfb-run ./out/Default/browser_tests --gtest_filter=NetworkingPrivate*'
Test: 'autoninja -C out/Default/ chrome/test:unit_tests && xvfb-run out/Default/unit_tests --gtest_filter=TrafficCountersHandlerTest.*'
Change-Id: Ie1d755fd34e9d37e5a969ab21d50a3155e48d352
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5420156
Commit-Queue: Kyle Williams <kdgwill@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1286095}
NOKEYCHECK=True
GitOrigin-RevId: 6bb2e71596cc9d4b1d5044b0d4027d3994f280ef
1 file changed