Allow mixed handler to handle transitions that might enter PIP

- The split transitions currently don't handle this case properly
  when an adjacent task is launched triggering a split task to
  enter PIP.

Fixes: 303755768
Test: Split YT & Gmail, click link from Gmail
Test: http://recall/-/g6hkB0pXjyQSvfA8STqRAT/hrdzWmMHFGHJKaSyLxb8yh
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6f1b98014920a36c55aa5110494f4428e038d51f)
Merged-In: I390ded4075211c8b5c0d328dcda42d189bee1fa8
Change-Id: I390ded4075211c8b5c0d328dcda42d189bee1fa8