[heap] Start concurrent marking simultaneously with incremental marking.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 63dfeecd4b674e8c23458d15d357b1a7fa687ba3..a7ae6b7f0a08d1b14d4575a9b01b3a681f45ac9c 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -648,6 +648,7 @@ DEFINE_BOOL(incremental_marking, true, "use incremental marking")
 DEFINE_BOOL(incremental_marking_wrappers, true,
             "use incremental marking for marking wrappers")
 DEFINE_BOOL(concurrent_marking, false, "use concurrent marking")
+DEFINE_BOOL(trace_concurrent_marking, false, "trace concurrent marking")
 DEFINE_INT(min_progress_during_incremental_marking_finalization, 32,
            "keep finalizing incremental marking as long as we discover at "
            "least this many unmarked objects")
@@ -1256,6 +1257,7 @@ DEFINE_VALUE_IMPLICATION(single_threaded, wasm_num_compilation_tasks, 0)
 
 DEFINE_BOOL(single_threaded, false, "disable the use of background tasks")
 DEFINE_NEG_IMPLICATION(single_threaded, concurrent_recompilation)
+DEFINE_NEG_IMPLICATION(single_threaded, concurrent_marking)
 DEFINE_NEG_IMPLICATION(single_threaded, concurrent_sweeping)
 DEFINE_NEG_IMPLICATION(single_threaded, parallel_compaction)
 DEFINE_NEG_IMPLICATION(single_threaded, concurrent_store_buffer)