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This CL adds a simple nullptr check to the web app menu for when the
browser window has no tabs selected.

Screenshot of no minor text:
https://bugs.chromium.org/p/chromium/issues/attachment?aid=457537&signed_aid=Kjcn9nX_y395O5ZsqKkjjw==&inline=1

Bug: 1103331
Change-Id: I79c2f02edebde35772f6cd7c34f8e8c610f56040
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2309769
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790585}