First take on custom call generators.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 18f45f3ba8a66516b1323dc51034d46e3e702753..4cc9b9f8340238549a12136218672eb205771007 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2361,8 +2361,7 @@ ACCESSORS(SharedFunctionInfo, construct_stub, Code, kConstructStubOffset)
 ACCESSORS(SharedFunctionInfo, name, Object, kNameOffset)
 ACCESSORS(SharedFunctionInfo, instance_class_name, Object,
           kInstanceClassNameOffset)
-ACCESSORS(SharedFunctionInfo, function_data, Object,
-          kExternalReferenceDataOffset)
+ACCESSORS(SharedFunctionInfo, function_data, Object, kFunctionDataOffset)
 ACCESSORS(SharedFunctionInfo, script, Object, kScriptOffset)
 ACCESSORS(SharedFunctionInfo, debug_info, Object, kDebugInfoOffset)
 ACCESSORS(SharedFunctionInfo, inferred_name, String, kInferredNameOffset)
@@ -2453,6 +2452,22 @@ bool SharedFunctionInfo::is_compiled() {
 }
 
 
+bool SharedFunctionInfo::IsApiFunction() {
+  return function_data()->IsFunctionTemplateInfo();
+}
+
+
+FunctionTemplateInfo* SharedFunctionInfo::get_api_func_data() {
+  ASSERT(IsApiFunction());
+  return FunctionTemplateInfo::cast(function_data());
+}
+
+
+bool SharedFunctionInfo::HasCustomCallGenerator() {
+  return function_data()->IsProxy();
+}
+
+
 bool JSFunction::IsBoilerplate() {
   return map() == Heap::boilerplate_function_map();
 }