GitLab

* Add `GetNodeIdByElement` to webView
* Add `ExecuteGetComputedLabel` to Element

Bug: chromedriver:3507
Change-Id: I53c558d73c57b588e27a8cc20c270619121d7fb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410392Reviewed-by: Shengfa Lin <shengfa@google.com>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Maksim Sadym <sadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807931}