[Read aloud] Fix bug where read aloud skips some gmail text.

The issue came because "in:draft" was identified as its original
node in app.ts, but read aloud used GetAnchor to reference the
parent when deciding whether or not it was text that should be spoken.

Bug: 396198522
Change-Id: I3f8f52b0cac38a27203eb060557df2ffc148c60e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6851872
Commit-Queue: Lauren Winston <lwinston@google.com>
Reviewed-by: Kristi Saney <kristislee@google.com>
Cr-Commit-Position: refs/heads/main@{#1501615}