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This change keeps the original transition type and adds
PAGE_TRANSITION_FORWARD_BACK as qualifier.

Change-Id: Ia3b59c3d555223a66a5553cbba2ff1ebf3b28f0c
Reviewed-on: https://chromium-review.googlesource.com/c/1371883Reviewed-by: Danyao Wang <danyao@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615817}