Introduce BeforeCallEnteredCallback.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index e0f2b1df329e7cb7dcb466ea3a242b6c2522b36c..f92ff4f58215ab36951d38b982ca353ff74003f2 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -2609,6 +2609,31 @@ Handle<JSObject> Isolate::GetSymbolRegistry() {
 }
 
 
+void Isolate::AddBeforeCallEnteredCallback(BeforeCallEnteredCallback callback) {
+  for (int i = 0; i < before_call_entered_callbacks_.length(); i++) {
+    if (callback == before_call_entered_callbacks_.at(i)) return;
+  }
+  before_call_entered_callbacks_.Add(callback);
+}
+
+
+void Isolate::RemoveBeforeCallEnteredCallback(
+    BeforeCallEnteredCallback callback) {
+  for (int i = 0; i < before_call_entered_callbacks_.length(); i++) {
+    if (callback == before_call_entered_callbacks_.at(i)) {
+      before_call_entered_callbacks_.Remove(i);
+    }
+  }
+}
+
+
+void Isolate::FireBeforeCallEnteredCallback() {
+  for (int i = 0; i < before_call_entered_callbacks_.length(); i++) {
+    before_call_entered_callbacks_.at(i)(reinterpret_cast<v8::Isolate*>(this));
+  }
+}
+
+
 void Isolate::AddCallCompletedCallback(CallCompletedCallback callback) {
   for (int i = 0; i < call_completed_callbacks_.length(); i++) {
     if (callback == call_completed_callbacks_.at(i)) return;