Fix vulnerability that allowed attackers to start arbitary activities

Test: Flashed device and verified dream settings works as expected
Test: Installed APK from bug and verified the dream didn't allow
launching the inappropriate settings activity.
Fixes: 300090204
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:bf8ff047eb25960720a688cb16aa44b3775799da)
Merged-In: I146415ad400827d0a798e27f34f098feb5e96422
Change-Id: I146415ad400827d0a798e27f34f098feb5e96422