[e2e] Simplify collectAllElementsFromPage helper
[e2e] Simplify collectAllElementsFromPage helper

This is a follow-up to [1].

[1]: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2007505/1/test/e2e/helper.ts#74

Bug: chromium:1044632
Change-Id: I1511c53393e9ec57e1c68085d06cf1c9841791fa
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2019140
Commit-Queue: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>
Commit-Queue: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>
Auto-Submit: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>
Reviewed-by: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend