ViewRootImpl: Always run finishBLASTSync

If we don't have any other commitCallbacks but we need to finish
a BLAST sync operation with SurfaceView, we still have to schedule
a frame complete callback. Also refactor the code a little to
remove some duplication.

Bug: 146598493
Test: Flip BLAST. Test Chrome.
Change-Id: I3475a45884fc13211e40613e316767addc286175