Execute non-optimized add operations one at a time.

Bug 34125817

It appears that some developers rely on fragment views containing
other fragments without using the fragment's child fragment manager.
This CL executes all unoptimized add operations separately to make
sure that this continues to work. Pop operations continue to be
executed together as they did previously.

Test: Ia0333ac1c09e18a6d9b08fe56b1e5c080652ab5b
Change-Id: I832fe631d05dbf8e9712899fef797da1f5747f5e