[heap] Start concurrent marking simultaneously with incremental marking.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index c56d3fbd01906639661171df9d6a072c408b12a3..25c4dd1fcf9d0b687f5b297056ca9846bfcae8f6 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -15,6 +15,7 @@
 #include "src/gdb-jit.h"
 #include "src/global-handles.h"
 #include "src/heap/array-buffer-tracker.h"
+#include "src/heap/concurrent-marking.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/mark-compact-inl.h"
@@ -780,6 +781,11 @@ void MarkCompactCollector::Prepare() {
   // them here.
   heap()->memory_allocator()->unmapper()->WaitUntilCompleted();
 
+  if (FLAG_concurrent_marking &&

[Hannes Payer (out of office), 2017/03/08 12:58:50]

Maybe we should have an EnsureMarkingCompleted() method then it would be similar
to sweeping.

[ulan, 2017/03/10 16:45:27]

Done.

+      heap()->concurrent_marking()->IsMarkingInProgress()) {
+    heap()->concurrent_marking()->WaitForTaskToComplete();
+  }
+
   // Clear marking bits if incremental marking is aborted.
   if (was_marked_incrementally_ && heap_->ShouldAbortIncrementalMarking()) {
     heap()->incremental_marking()->Stop();