GitLab

These are simply convenience methods to avoid repeating
this.shadowRoot.querySelector() and this.shadowRoot.querySelectorAll().

Bug: None
Change-Id: I850c7953a258feeede334687069f0a0764b698e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2021189
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735567}