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This is a reland of 90c5851b

ASan failures fixed in http://crrev.com/c/1887830

Original change's description:
> [WebLayer] Add tests for chrome://weblayer page
>
> This page recently broke (fix in http://crrev.com/c/1880171), so tests
> seem like a good idea.
>
> This also adds a test helper for executing javascript, and makes the
> NavigateAndWaitForCompletion function work more similarly to the one in
> the instrumentation tests by waiting until the page is finished loading.
>
> Bug: 1017924
> Change-Id: I8ca048f9a9a92808abf6cfa5d0e091550cc3d9a6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880173
> Commit-Queue: Clark DuVall <cduvall@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#709552}

TBR=sky@chromium.org

Bug: 1017924
Change-Id: I249d22946e0bb240e32d38c33637c73bf6c63fe0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887725Reviewed-by: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710506}