Added parallel marking threads.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 23e1f2c8fe9096e73d0031c2615850e2c46c75e5..df70ba9efd4b4198b7ee28b94da4b60287f5c1d3 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -71,6 +71,7 @@ class HeapProfiler;
 class InlineRuntimeFunctionsTable;
 class NoAllocationStringAllocator;
 class InnerPointerToCodeCache;
+class MarkingThread;
 class PreallocatedMemoryThread;
 class RegExpStack;
 class SaveContext;
@@ -1074,6 +1075,10 @@ class Isolate {
   // TODO(svenpanne) This method is on death row...
   static v8::Isolate* GetDefaultIsolateForLocking();
 
+  MarkingThread** marking_threads() {
+    return marking_thread_;
+  }
+
   SweeperThread** sweeper_threads() {
     return sweeper_thread_;
   }
@@ -1301,11 +1306,13 @@ class Isolate {
 
   DeferredHandles* deferred_handles_head_;
   OptimizingCompilerThread optimizing_compiler_thread_;
+  MarkingThread** marking_thread_;
   SweeperThread** sweeper_thread_;
 
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;
   friend class IsolateInitializer;
+  friend class MarkingThread;
   friend class OptimizingCompilerThread;
   friend class SweeperThread;
   friend class ThreadManager;