Implement callback when script finishes running in V8 API.

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index b16e7396ad45e6410ee96066fead715aad75cd3b..628a19825b1a6078f0af22a69290c9ca1ee5d54f 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -107,6 +107,7 @@ static Handle<Object> Invoke(bool is_construct,
     // allocation of handles without explicit handle scopes.
     SaveContext save(isolate);
     NoHandleAllocation na;
+    // Increase call depth and fire callbacks after the call if applicable.
     JSEntryFunction stub_entry = FUNCTION_CAST<JSEntryFunction>(code->entry());
 
     // Call the function through the right JS entry stub.