✅ Deflakes SwG E2E Test

[ChrisAntaki]

This PR deflakes the SwG E2E test by waiting for the SwG button to render before triggering a click.

[jridgewell]

LGTM, but need @chenshay's review.

[rsimha]

@ChrisAntaki Thanks for fixing our tests! Looks like it failed on master again? https://travis-ci.org/ampproject/amphtml/jobs/599341253#L575

[ChrisAntaki]

It doesn't repro often locally, but when it does here's what I see:

error.js:195 Service  subscriptions was requested to be provided through amp-subscriptions , but amp-subscriptions is not loaded in the current page. To fix this problem load the JavaScript file for amp-subscriptions in this page.
nf @ error.js:195
(anonymous) @ error.js:128
f.assert @ log.js:428
ja @ log.js:988
(anonymous) @ element-service.js:186
log.js:422 Uncaught (in promise) Error: Service subscriptions was requested to be provided through amp-subscriptions, but amp-subscriptions is not loaded in the current page. To fix this problem load the JavaScript file for amp-subscriptions in this page.​​​
    at Wa.f.assert (log.js:422)
    at ja (log.js:988)
    at element-service.js:186
f.assert @ log.js:422
ja @ log.js:988
(anonymous) @ element-service.js:186

[ChrisAntaki]

Here are the complete logs from a failed run. Interestingly, the amp-subscriptions plugin does seem to kick off a request (which is expected to fail) later, so it does load eventually. Perhaps there's a race condition with the loading of extensions?

amp.js:157 Powered by AMP ⚡ HTML – Version 1910172338580 http://localhost:8000/test/fixtures/e2e/amp-subscriptions-google/swg.amp.html
error.js:195 Service  subscriptions was requested to be provided through amp-subscriptions , but amp-subscriptions is not loaded in the current page. To fix this problem load the JavaScript file for amp-subscriptions in this page.
nf @ error.js:195
(anonymous) @ error.js:128
f.assert @ log.js:428
ja @ log.js:988
(anonymous) @ element-service.js:186
log.js:422 Uncaught (in promise) Error: Service subscriptions was requested to be provided through amp-subscriptions, but amp-subscriptions is not loaded in the current page. To fix this problem load the JavaScript file for amp-subscriptions in this page.​​​
    at Wa.f.assert (log.js:422)
    at ja (log.js:988)
    at element-service.js:186
f.assert @ log.js:422
ja @ log.js:988
(anonymous) @ element-service.js:186
:8000/examples/sample-pub/amp-entitlements?pubid=com.appspot.scenic-2017&meter=1&__amp_source_origin=http%3A%2F%2Flocalhost%3A8000:1 Failed to load resource: the server responded with a status of 404 (Not Found)
log.js:244 [amp-subscriptions] Local platform has failed to resolve,  using fallback entitlement.
Ya @ log.js:244
f.warn @ log.js:285
push.f.h.reportPlatformFailureAndFallback @ platform-store.js:598
(anonymous) @ amp-subscriptions.js:304
error.js:202 fetch entitlements failed for local: HTTP error 404​​​
nf @ error.js:202
(anonymous) @ error.js:294
log.js:707 Uncaught (in promise) Error: fetch entitlements failed for local: HTTP error 404​​​
    at $a (log.js:707)
    at Wa.f.createError (log.js:345)
    at xhr-utils.js:385
    at new Promise (<anonymous>)
    at ig (xhr-utils.js:379)
    at xhr-impl.js:158
$a @ log.js:707
f.createError @ log.js:345
(anonymous) @ xhr-utils.js:385
ig @ xhr-utils.js:379
(anonymous) @ xhr-impl.js:158
cdn.ampproject.org/rtv/011910172338580/v0/amp-auto-lightbox-0.1.js:1 Failed to load resource: the server responded with a status of 404 ()
:8000/favicon.ico:1 Failed to load resource: the server responded with a status of 404 (Not Found)

[ChrisAntaki]

@jpettitt has the real fix in #25145