Set mSyncBuffer to true when VRI did not initiate the sync request

VRI can initiate syncs, but they can also happen from other places when
using SurfaceSyncer. When VRI initiates the sync, sometimes the buffer
needs to be synced. Other times, we just want to know the buffer has
drawn, but don't actually need to sync the buffer.

When a sync is initiated from outside VRI, using SurfaceSyncer, we
always want to sync the buffer. This change ensures that if the sync was
started from an outside request, it will set mSyncBuffer to true.

An additional part to clarify the sync logic, renamed mLastSyncId to
mSyncId and renamed isInSync to isInLocalSync to clarify that the
mSyncId only represents VRI initiated syncs.

Test: Internet Dialog syncs buffer
Fixes: 229098223
Change-Id: I99e9e6341a487d59c33a33a61e442be7909518c2