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This is a reland of 3692f7b0

Adds a missing GN dep which caused a build breakage on component/debug
builds.

Original change's description:
> [web_engine] Add "web_engine_shell" standalone executable.
>
> Implements a simple standalone executable which will launch a fullscreen
> browsing session and navigate it to a given URL. Similar to
> content_shell, but using Web Engine instead.
>
> The flow is kept deliberately simple and linear so it can serve as a
> functioning code sample for aspiring embedders of Web Engine.
>
> The shell can be used to test arbitrary static data, which is sourced
> from //fuchsia/engine/test/shell_data and hosted under the content URL
> fuchsia-dir://shell-data/ .
>
> The shell can also optionally request that the DevTools server be
> started at a port specified on the command line.
>
> Bug: 1016485
> Change-Id: I09ad56f20553acc83fbf38924fa3e8d8a98a1200
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869887
> Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
> Reviewed-by: David Dorwin <ddorwin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#707911}

TBR=ddorwin@chromium.org

Bug: 1016485
Change-Id: I49728ffa5ab21e8a329bd8e1fefdb1071460ef4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872827Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708009}