It happens that a scavenger runs during incremental marking. Currently scavenger does not care about MarkCompact's mark bits. When an object is alive and marked, and at least one scavenge happens during incremental marking, the object will be copied once to the other semispace in the new_space, and then once to the old_space. For surviving objects this is useless extra work.

In our current attempts (https://codereview.chromium.org/1988623002) to ensure marked objects are scavenged, all marked objects will survive therefore there will be many objects which will be uselessly copied.

This cl modifies our promotion logic so when incremental marking is in progress, and the object is marked, we promote it unconditionally.

BUG=
LOG=no

Review-Url: https://codereview.chromium.org/2005173003
Cr-Commit-Position: refs/heads/master@{#36643}