Enable parallel pointer updates after evacuation.

BUG=chromium:578883
LOG=NO

Review URL: https://codereview.chromium.org/1784643010

Cr-Commit-Position: refs/heads/master@{#34712}

src/flag-definitions.h

@@ -690,7 +690,7 @@ DEFINE_INT(max_incremental_marking_finalization_rounds, 3,
            "at most try this many times to finalize incremental marking")
 DEFINE_BOOL(concurrent_sweeping, true, "use concurrent sweeping")
 DEFINE_BOOL(parallel_compaction, true, "use parallel compaction")
-DEFINE_BOOL(parallel_pointer_update, false,
+DEFINE_BOOL(parallel_pointer_update, true,
             "use parallel pointer update during compaction")
 DEFINE_BOOL(trace_incremental_marking, false,
             "trace progress of the incremental marking")