[heap] Disable compaction for concurrent marking.

7a5a777c is going to be reverted and compaction depends on it.

BUG=chromium:694255
TBR=ulan@chromium.org,mlippautz@chromium.org

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I975ea597860dd63e543b69bdc787c6667b015567
Reviewed-on: https://chromium-review.googlesource.com/595993
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47053}

src/flag-definitions.h

@@ -678,6 +678,9 @@ DEFINE_INT(v8_os_page_size, 0, "override OS page size (in KBytes)")
 DEFINE_BOOL(always_compact, false, "Perform compaction on every full GC")
 DEFINE_BOOL(never_compact, false,
             "Never perform compaction on full GC - testing only")
+// TODO(ulan): enable compaction for concurrent marking when it correctly
+// records slots to evacuation candidates.
+DEFINE_IMPLICATION(concurrent_marking, never_compact)
 DEFINE_BOOL(compact_code_space, true, "Compact code space on full collections")
 DEFINE_BOOL(cleanup_code_caches_at_gc, true,
             "Flush code caches in maps during mark compact cycle.")