Add the rate of js invocations from the api as a signal of idleness

src/isolate.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include <queue>
 #include <set>
 
@@ skipping 1028 matching lines @@
   Object* FindCodeObject(Address a);
 
   int NextOptimizationId() {
     int id = next_optimization_id_++;
     if (!Smi::IsValid(next_optimization_id_)) {
       next_optimization_id_ = 0;
     }
     return id;
   }
 
+  void IncrementJsCallsFromApiCounter() { ++js_calls_from_api_counter_; }
+
+  unsigned int js_calls_from_api_counter() {
+    return js_calls_from_api_counter_;
+  }
+
   // Get (and lazily initialize) the registry for per-isolate symbols.
   Handle<JSObject> GetSymbolRegistry();
 
   void AddCallCompletedCallback(CallCompletedCallback callback);
   void RemoveCallCompletedCallback(CallCompletedCallback callback);
   void FireCallCompletedCallback();
 
   void SetPromiseRejectCallback(PromiseRejectCallback callback);
   void ReportPromiseReject(Handle<JSObject> promise, Handle<Object> value,
                            v8::PromiseRejectEvent event);
@@ skipping 247 matching lines @@
   OptimizingCompileDispatcher* optimizing_compile_dispatcher_;
 
   // Counts deopt points if deopt_every_n_times is enabled.
   unsigned int stress_deopt_count_;
 
   Address virtual_handler_register_;
   Address virtual_slot_register_;
 
   int next_optimization_id_;
 
+  // Counts javascript calls from the API. Wraps around on overflow.
+  unsigned int js_calls_from_api_counter_;
+
 #if TRACE_MAPS
   int next_unique_sfi_id_;
 #endif
 
   // List of callbacks when a Call completes.
   List<CallCompletedCallback> call_completed_callbacks_;
 
   v8::Isolate::UseCounterCallback use_counter_callback_;
   BasicBlockProfiler* basic_block_profiler_;
 
@@ skipping 230 matching lines @@
 
   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ISOLATE_H_