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This is a reland of 9869d2f1

I've marked the tests as Slow in this CL (https://chromium-review.googlesource.com/c/600829)
which is why there were flaky before.

Original change's description:
> DevTools: transform console tests (part 2)
> 
> F/u from https://chromium-review.googlesource.com/c/595238
> 
> Bug: 667560
> Change-Id: I4e387fae79ab4de0965f84a045c4fd04631b9e7d
> Reviewed-on: https://chromium-review.googlesource.com/597312
> Commit-Queue: Will Chen <chenwilliam@chromium.org>
> Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#491501}

Bug: 667560
Change-Id: Ie2cc4dd1249b46b7ce784a516647acaee223c39f
Reviewed-on: https://chromium-review.googlesource.com/600814Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Will Chen <chenwilliam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491884}