Make number of available threads isolate-dependent and expose it to ResourceConstraints.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 0570557369313d8a7b055c9ecd50af5455be8f96..752a1ed73760d0bc92ac0f8586eb05cad6471a47 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1699,12 +1699,7 @@ class Heap {
            old_pointer_space()->IsLazySweepingComplete();
   }
 
-  bool AdvanceSweepers(int step_size) {
-    ASSERT(!FLAG_parallel_sweeping && !FLAG_concurrent_sweeping);
-    bool sweeping_complete = old_data_space()->AdvanceSweeper(step_size);
-    sweeping_complete &= old_pointer_space()->AdvanceSweeper(step_size);
-    return sweeping_complete;
-  }
+  bool AdvanceSweepers(int step_size);
 
   bool EnsureSweepersProgressed(int step_size) {
     bool sweeping_complete = old_data_space()->EnsureSweeperProgress(step_size);
@@ -1833,23 +1828,19 @@ class Heap {
   // only when FLAG_concurrent_recompilation is true.
   class RelocationLock {
    public:
-    explicit RelocationLock(Heap* heap);
+    explicit RelocationLock(Heap* heap) : heap_(heap) {
+      if (FLAG_concurrent_recompilation) {
+        heap_->relocation_mutex_->Lock();
+      }
+    }
+
 
     ~RelocationLock() {
       if (FLAG_concurrent_recompilation) {
-#ifdef DEBUG
-        heap_->relocation_mutex_locked_by_optimizer_thread_ = false;
-#endif  // DEBUG
         heap_->relocation_mutex_->Unlock();
       }
     }
 
-#ifdef DEBUG
-    static bool IsLockedByOptimizerThread(Heap* heap) {
-      return heap->relocation_mutex_locked_by_optimizer_thread_;
-    }
-#endif  // DEBUG
-
    private:
     Heap* heap_;
   };