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This is a reland of 7cfe51d0

The build error should be fixed by https://crrev.com/c/2416892

Original change's description:
> [WebLayer] Enable WebLayer in split on canary
>
> This enables WebLayer in a split in WebView bundles in canary. I tested
> on L-Q and ran all instrumentation tests on P with this setup.
>
> Bug: 1105096
> Change-Id: I517bce4109531108a4fb3af64a87aa1f5d2a91bb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412705
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Clark DuVall <cduvall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#807252}

Bug: 1105096
Change-Id: I0d179670f0979809866ae278d7a4e6fd7a58dfbe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416878Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807995}