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

src/api.cc

 // 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.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 140 matching lines @@
 class CallDepthScope {
  public:
   explicit CallDepthScope(i::Isolate* isolate, Local<Context> context,
                           bool do_callback)
       : isolate_(isolate),
         context_(context),
         escaped_(false),
         do_callback_(do_callback) {
     // TODO(dcarney): remove this when blink stops crashing.
     DCHECK(!isolate_->external_caught_exception());
+    isolate_->IncrementJsCallsFromApiCounter();
     isolate_->handle_scope_implementer()->IncrementCallDepth();
     if (!context_.IsEmpty()) context_->Enter();
   }
   ~CallDepthScope() {
     if (!context_.IsEmpty()) context_->Exit();
     if (!escaped_) isolate_->handle_scope_implementer()->DecrementCallDepth();
     if (do_callback_) isolate_->FireCallCompletedCallback();
   }
 
   void Escape() {
@@ skipping 8291 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8