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In the multi-WebContents implementation, history must be copied from
the old WebContents's NavigationController.

Also adjust a unittest to more fully simulate navigation, as it's
necessary to commit the navigation in order to copy the history.

Bug: 1132746
Change-Id: I0e2061451779d1fa9e4db2957aa06d0a05bef436
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2612291Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841405}