Enabled back button for HTMLViewer activity. This allows users to exit
the activity easily without having to go through hardware/software back
buttons.

Bug: 143491123, 146164760
Test: Manual
Change-Id: Id248fb01882c668a752d1dde871e9a7bf2d63431
(cherry picked from commit 2b81eb2d44667c02d5d614f20cbf0ef3652844a1)
Merged-In: : Id248fb01882c668a752d1dde871e9a7bf2d63431
1 file changed