Reland "SurfaceControlViewHost: Restrict disclosure of input token""

The original CL only updated one of the two implementations of
grantEmbeddedWindowFocus, and for as of yet unknown reasons
presubmit did not detect the failure until after it landed.

Bug: 215912712
Test: SurfaceControlViewHostTests
Change-Id: Ie278f678f12f50c32f142a4260ff7d1c2a9ca57c