Handle multiple relayout calls with blast sync

The issue is the following:
1. Call relayout from VRI. drawsNeededToReport = 1
2. SV also will need to be updated. drawsNeedToReport = 2
3. VRI is finished rendering, but SV is not. drawsNeedToReport = 1
4. VRI calls relayout again. drawsNeedToReport = 2
5. SV finishes drawing. drawsNeedToReport = 1

BBQ will get stuck since it's waiting indefinitey for a transaction
callback. The previous transaction can never get applied since we're
still waiting until drawsNeededToReport = 0.

This prevents situations like this from happening since it will not
allow a relayout to get called until the previous transaction has been
applied.

Test: Split screen with chrome
Bug: 167202096
Change-Id: I167a90ef00fa6677b3c55239e74eefb6a1384baf