Ned, what do you think? Would it be OK to patch the pageScaleFactor on Telemetry js scripts with a fallback to "degrade gracefully" when the function does not exist?

Or maybe some other alternative?

Patching it is OK to me, but you may want to have a more systematic look at what other methods are not available in chrome.gpuBenchmarking.* that are required for action_runner implementation.

I suggest running all the unittests in src/third_party/catapult/telemetry/telemetry/internal/actions/* for Chrome 40s & see which one fails

pageScaleFactor is now fixed by:
https://chromium-review.googlesource.com/c/catapult/+/1161930

Still to confirm whether all other telemetry.internal.actions.* tests pass on older Chrome versions.

After running all the tests in telemetry.internal.actions.*, here is the
tests that didn't passed:

-
`telemetry.internal.actions.pinch_unittest.PinchActionTest.testPinchAnchor`
and some other tests that needs to use the `Window.visualViewport`, however
this API is introduced after M60,  see:
https://developer.mozilla.org/en-US/docs/Web/API/Window/visualViewport, and
it is only used in unittest, so I think we don't need to take any action
for that.

-
`telemetry.internal.actions.scroll_unittest.ScrollActionTest.testBoundingClientRect'
failed
because `EvaluateException: Uncaught TypeError:
chrome.gpuBenchmarking.visualViewportX is not a function`
This is address in the CL:
https://chromium-review.googlesource.com/c/catapult/+/1167296

-
`telemetry.internal.actions.play_unittest.PlayActionTest.testPlayWithAllSelector`,
and the failing reason is that 'TimeoutException: Timed out while waiting
5s for lambda: self.HasEventCompletedOrError(tab, selector, event_name)',
the same failing reasons also occur in some other test cases which I didn't
list here.

-
`telemetry.internal.actions.action_runner_unittest.ActionRunnerMeasureMemoryTest.testDeterministicMode`
failed, says that 'list indices need to be integer instead of string'