Oilpan: Scale up the number of marking threads according to available processors

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index 4d10b2fc376de5b42420c025b53c9f188e0abcc6..175469933d12abe2c13e0d9218952e04f218beb7 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -94,7 +94,7 @@ const uint8_t finalizedZapValue = 24;
 // the mark bit when tracing.
 const uint8_t orphanedZapValue = 240;
 
-const int numberOfMarkingThreads = 2;
+const int maxNumberOfMarkingThreads = 4;
 
 const int numberOfPagesToConsiderForCoalescing = 100;
 
@@ -959,7 +959,7 @@ public:
     static void collectGarbage(ThreadState::StackState, ThreadState::CauseOfGC = ThreadState::NormalGC);
     static void collectGarbageForTerminatingThread(ThreadState*);
     static void collectAllGarbage();
-    static void processMarkingStackEntries(int* numberOfMarkingThreads);
+    static void processMarkingStackEntries(int*);
     static void processMarkingStackOnMultipleThreads();
     static void processMarkingStackInParallel();
     template<CallbackInvocationMode Mode> static void processMarkingStack();