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This CL changes the stored data scheme of the web payment app,
so users have to re-register the web payment app after this patch.

This should be fine since this feature is still behind the flag. 

Bug: 751737
Change-Id: I396960273dca51f82a4490fa2dd5f7756e3a0bf0
Reviewed-on: https://chromium-review.googlesource.com/598636
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491742}