Convert editing/pasteboard/3976872.html to use w3c test harness
This patch converts "editing/pasteboard/3976872.html" to use w3c test harness to
simplify test script, and renames to "paste_plain_text_to_newlines.html" to
provide a hint what this test script verifies, for improving code health.
BUG=n/a
TEST=n/a; no behavior changes
Committed:
https://crrev.com/b5bc3aa80a4acd3a2e67194d25922153e5ccd19b
Cr-Commit-Position: refs/heads/master@{#419116}