Revert "Blocks backspace to prevent returning to preview page."

This reverts commit 45788e06527cd44869f74d6b84063a1cc4f4eefc.

Change-Id: I26b6e2c408da4e8e9c7dc9443b3a12f7e9bc34a1
Reviewed-on: https://chromium-review.googlesource.com/176197
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Tested-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Ricky Liang <jcliang@chromium.org>
1 file changed