Introduce BeforeCallEnteredCallback.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index b7dcd446c154e9d232ada47575fe5c227775e07a..767cc61bc702c457385c900044717d51d6597f47 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -164,6 +164,7 @@ class CallDepthScope {
         do_callback_(do_callback) {
     // TODO(dcarney): remove this when blink stops crashing.
     DCHECK(!isolate_->external_caught_exception());
+    if (do_callback_) isolate_->FireBeforeCallEnteredCallback();

[dgozman, 2016/02/11 02:08:49]

I think I'd move this call after context->Enter() so that embedder can check in
which context we are about to execute.

     isolate_->IncrementJsCallsFromApiCounter();
     isolate_->handle_scope_implementer()->IncrementCallDepth();
     if (!context_.IsEmpty()) context_->Enter();
@@ -7371,6 +7372,20 @@ void Isolate::SetEventLogger(LogEventCallback that) {
 }
 
 
+void Isolate::AddBeforeCallEnteredCallback(BeforeCallEnteredCallback callback) {
+  if (callback == NULL) return;
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  isolate->AddBeforeCallEnteredCallback(callback);
+}
+
+
+void Isolate::RemoveBeforeCallEnteredCallback(
+    BeforeCallEnteredCallback callback) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  isolate->RemoveBeforeCallEnteredCallback(callback);
+}
+
+
 void Isolate::AddCallCompletedCallback(CallCompletedCallback callback) {
   if (callback == NULL) return;
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);