[heap] Reland Use atomic marking operations in incremental marking if

concurrent marking is enabled.

This patch adds kAtomicity flag to IncrementalMarking that is set
depending on the concurrent marking compile time flag.

BUG=chromium:694255
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_rel_ng

Review-Url: https://codereview.chromium.org/2858343003
Cr-Commit-Position: refs/heads/master@{#45138}

src/heap/incremental-marking.h

@@ -182,6 +182,12 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
   static const intptr_t kActivationThreshold = 0;
 #endif
 
+#if V8_CONCURRENT_MARKING
+  static const MarkBit::AccessMode kAtomicity = MarkBit::AccessMode::ATOMIC;
+#else
+  static const MarkBit::AccessMode kAtomicity = MarkBit::AccessMode::NON_ATOMIC;
+#endif
+
   void FinalizeSweeping();
 
   size_t Step(size_t bytes_to_process, CompletionAction action,