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This is the second CL of several breaking crrev.com/c/1860025 into smaller
chunks.

Change the various classes and tests in ui/first_run/ to accept a Browser
where before they accepted a BrowserState. Spurious use of, and dependency
on, TabModel is also removed.

Change-Id: I961a684231d78036881084be0222d56787a55e9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863017
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709840}