Async Clipboard: Add missing return statement.

A missing return statement caused a write() to continue even after it should
have returned a DOMException and error'ed out. This adds the return back in.

Bug: 940222
Change-Id: I1d4ac663cfe03e1c6c738f17d75691318efba81e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1516260
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639758}
1 file changed