Revert "Remove FLAG_ACTIVITY_FORWARD_RESULT in 2-pane flow"

This reverts commit ea1580f9.

Reason for revert:
1. Search result trampoline should have that result sent back to the
reply target of the original activity.
2. To leverage the behavior of handheld's deep link case, large
screen's deep link should forward the result.

Change-Id: I55303070e35fc9430063655e0a9a0fd72e0823ac