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

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index fa16f31481bdc63dc5ed553cbdf63abf6f063746..86266be225984b14903713e7063ef9b6da95e351 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -158,6 +158,7 @@ class CallDepthScope {
         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();
   }