Make deoptimization stress count global.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index c0ea772d1fa0000015fcda22bd4ae15de5bbc7f5..b3651e16e96738b8427c243278c69c57bb314073 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1130,6 +1130,8 @@ class Isolate {
     function_entry_hook_ = function_entry_hook;
   }
 
+  void* stress_deopt_count_address() { return &stress_deopt_count_; }
+
  private:
   Isolate();
 
@@ -1365,6 +1367,9 @@ class Isolate {
   SweeperThread** sweeper_thread_;
   CallbackTable* callback_table_;
 
+  // Counts deopt points if deopt_every_n_times is enabled.
+  unsigned int stress_deopt_count_;
+
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;
   friend class IsolateInitializer;