Simplify invokeCallback() and support void return values for IDL callbacks

Source/bindings/v8/custom/V8SQLTransactionCustom.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 78 matching lines @@
     SQLTransaction* transaction = V8SQLTransaction::toNative(info.Holder());
 
     ExecutionContext* executionContext = getExecutionContext();
 
     OwnPtr<SQLStatementCallback> callback;
     if (info.Length() > 2 && !isUndefinedOrNull(info[2])) {
         if (!info[2]->IsFunction()) {
             setDOMException(TypeMismatchError, info.GetIsolate());
             return;
         }
-        callback = V8SQLStatementCallback::create(v8::Handle<v8::Object>::Cast(info[2]), executionContext);
+        callback = V8SQLStatementCallback::create(v8::Handle<v8::Function>::Cast(info[2]), executionContext);
     }
 
     OwnPtr<SQLStatementErrorCallback> errorCallback;
     if (info.Length() > 3 && !isUndefinedOrNull(info[3])) {
         if (!info[3]->IsFunction()) {
             setDOMException(TypeMismatchError, info.GetIsolate());
             return;
         }
-        errorCallback = V8SQLStatementErrorCallback::create(v8::Handle<v8::Object>::Cast(info[3]), executionContext);
+        errorCallback = V8SQLStatementErrorCallback::create(v8::Handle<v8::Function>::Cast(info[3]), executionContext);
     }
 
     ExceptionState exceptionState(info.Holder(), info.GetIsolate());
     transaction->executeSQL(statement, sqlValues, callback.release(), errorCallback.release(), exceptionState);
     exceptionState.throwIfNeeded();
 }
 
 } // namespace WebCore