Add ScopedTrace in MarkCompact::PrepareForCompaction()

This is to detect if the cause of long running GCs sometime when
preparing for compaction. This function is not expected to take very
long so we can revert this CL afterwards.

Test: manual
Bug: 340644226
Change-Id: Ibda6f21bd989120fc9a9be9f50a332ad3b00147d
1 file changed