Remove parallel marking support.

src/v8.cc

Index: src/v8.cc
diff --git a/src/v8.cc b/src/v8.cc
index e894164cd16207448befdc3c0daa93bf08c315bc..62330c32d482aa9a1a74ba70f38d769bfff240da 100644
--- a/src/v8.cc
+++ b/src/v8.cc
@@ -227,19 +227,6 @@ void V8::InitializeOncePerProcessImpl() {
     FLAG_sweeper_threads = 0;
   }
 
-  if (FLAG_parallel_marking) {
-    if (FLAG_marking_threads <= 0) {
-      FLAG_marking_threads = SystemThreadManager::
-          NumberOfParallelSystemThreads(
-              SystemThreadManager::PARALLEL_MARKING);
-    }
-    if (FLAG_marking_threads == 0) {
-      FLAG_parallel_marking = false;
-    }
-  } else {
-    FLAG_marking_threads = 0;
-  }
-
   if (FLAG_concurrent_recompilation &&
       SystemThreadManager::NumberOfParallelSystemThreads(
           SystemThreadManager::PARALLEL_RECOMPILATION) == 0) {