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Instead of accessing the ReaderModeManager via Tab and ChromeActivity,
a reference to the manager is passed to the native infobar when it is
created and pulled back up to java when needed. This also allowed for
the removal of the GetTab native method.

Bug: 952703
Change-Id: Iaacbbda08e28d013538d44c9b985020c175de1be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2122471
Commit-Queue: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Auto-Submit: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754230}