This seems to have started around https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Fuchsia%20x64/14471.

[ RUN      ] InputRouterImplTest.GestureTypesIgnoringAck
../../content/browser/renderer_host/input/input_router_impl_unittest.cc:818: Failure
Expected equality of these values:
  0
  client_->in_flight_event_count()
    Which is: 1
Stack trace:
bt#00: pc 0x577a69102a36 (app:/pkg/bin/app,0x332da36)
bt#01: pc 0x577a691023db (app:/pkg/bin/app,0x332d3db)
bt#02: pc 0x577a681b4bcc (app:/pkg/bin/app,0x23dfbcc)
bt#03: end
../../content/browser/renderer_host/input/input_router_impl_unittest.cc:819: Failure
Value of: HasPendingEvents()
  Actual: true
Expected: false
Stack trace:
bt#00: pc 0x577a69102a36 (app:/pkg/bin/app,0x332da36)
bt#01: pc 0x577a691023db (app:/pkg/bin/app,0x332d3db)
bt#02: pc 0x577a681b4cd1 (app:/pkg/bin/app,0x23dfcd1)
bt#03: end
../../content/browser/renderer_host/input/input_router_impl_unittest.cc:814: Failure
Expected equality of these values:
  2U
    Which is: 2
  disposition_handler_->GetAndResetAckCount()
    Which is: 1
Stack trace:
bt#00: pc 0x577a69102a36 (app:/pkg/bin/app,0x332da36)
bt#01: pc 0x577a691023db (app:/pkg/bin/app,0x332d3db)
bt#02: pc 0x577a681b4ab9 (app:/pkg/bin/app,0x23dfab9)
bt#03: end
[  FAILED  ] InputRouterImplTest.GestureTypesIgnoringAck (10 ms)

https://chromium.googlesource.com/chromium/src/+/49d91137f863ad41e769ac4eb8f3ce5296c98fd9 is a likely culprit landed around the same time. sahel@ can you PTAL? I am going to disable the flaky test on Fuchsia for now.