[heap] Introduce a flag for enabling parallel marking in atomic pause.

The flag is --parallel-marking.

Bug: chromium:750084
Change-Id: I20ab5945d2cc41d44b29d7090a3436d028588540
Reviewed-on: https://chromium-review.googlesource.com/756709Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49178}

src/flag-definitions.h

@@ -623,6 +623,8 @@ DEFINE_BOOL(write_protect_code_memory, false, "write protect code memory")
 #endif
 DEFINE_BOOL(concurrent_marking, V8_CONCURRENT_MARKING_BOOL,
             "use concurrent marking")
+DEFINE_BOOL(parallel_marking, false, "use parallel marking in atomic pause")
+DEFINE_IMPLICATION(parallel_marking, concurrent_marking)
 DEFINE_BOOL(trace_concurrent_marking, false, "trace concurrent marking")
 DEFINE_BOOL(minor_mc_parallel_marking, true,
             "use parallel marking for the young generation")
@@ -650,6 +652,7 @@ DEFINE_VALUE_IMPLICATION(track_gc_object_stats, gc_stats, 1)
 DEFINE_VALUE_IMPLICATION(trace_gc_object_stats, gc_stats, 1)
 DEFINE_NEG_IMPLICATION(trace_gc_object_stats, incremental_marking)
 DEFINE_NEG_IMPLICATION(track_retaining_path, incremental_marking)
+DEFINE_NEG_IMPLICATION(track_retaining_path, parallel_marking)
 DEFINE_NEG_IMPLICATION(track_retaining_path, concurrent_marking)
 DEFINE_BOOL(track_detached_contexts, true,
             "track native contexts that are expected to be garbage collected")
@@ -1244,6 +1247,7 @@ DEFINE_BOOL(single_threaded_gc, false, "disable the use of background gc tasks")
 DEFINE_NEG_IMPLICATION(single_threaded_gc, concurrent_marking)
 DEFINE_NEG_IMPLICATION(single_threaded_gc, concurrent_sweeping)
 DEFINE_NEG_IMPLICATION(single_threaded_gc, parallel_compaction)
+DEFINE_NEG_IMPLICATION(single_threaded_gc, parallel_marking)
 DEFINE_NEG_IMPLICATION(single_threaded_gc, parallel_pointer_update)
 DEFINE_NEG_IMPLICATION(single_threaded_gc, parallel_scavenge)
 DEFINE_NEG_IMPLICATION(single_threaded_gc, concurrent_store_buffer)

src/heap/mark-compact.cc

@@ -2529,7 +2529,8 @@ void MarkCompactCollector::MarkLiveObjects() {
 
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_MAIN);
-    if (FLAG_concurrent_marking) {
+    if (FLAG_parallel_marking) {
+      DCHECK(FLAG_concurrent_marking);
       heap_->concurrent_marking()->RescheduleTasksIfNeeded();
     }
     ProcessMarkingWorklist();