Check for validity when accessing call site objects in runtime.

src/messages.h

 // Copyright 2006-2008 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.
 
 // The infrastructure used for (localized) message reporting in V8.
 //
 // Note: there's a big unresolved issue about ownership of the data
 // structures used by this framework.
 
 #ifndef V8_MESSAGES_H_
@@ skipping 44 matching lines @@
   Handle<Object> GetMethodName();
   // Return 1-based line number, including line offset.
   int GetLineNumber();
   // Return 1-based column number, including column offset if first line.
   int GetColumnNumber();
   bool IsNative();
   bool IsToplevel();
   bool IsEval();
   bool IsConstructor();
 
+  bool IsValid() { return !fun_.is_null(); }
+
  private:
   Isolate* isolate_;
   Handle<Object> receiver_;
   Handle<JSFunction> fun_;
   int pos_;
 };
 
 
 #define MESSAGE_TEMPLATES(T)                                                   \
   /* Error */                                                                  \
@@ skipping 417 matching lines @@
   static MUST_USE_RESULT MaybeHandle<String> GetStringifiedProperty(
       Isolate* isolate, LookupIterator* property_lookup,
       Handle<String> default_value);
 
   List<Handle<JSObject> > visited_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_