Revert of Have postMessage()s throw TypeError on failed arity checks.

Source/bindings/core/v8/custom/V8WindowCustom.cpp

 /*
  * Copyright (C) 2009, 2011 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 141 matching lines @@
 static bool isLegacyTargetOriginDesignation(v8::Handle<v8::Value> value)
 {
     if (value->IsString() || value->IsStringObject())
         return true;
     return false;
 }
 
 
 void V8Window::postMessageMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
-    ExceptionState exceptionState(ExceptionState::ExecutionContext, "postMessage", "Window", info.Holder(), info.GetIsolate());
-    if (UNLIKELY(info.Length() < 2)) {
-        setMinimumArityTypeError(exceptionState, 2, info.Length());
-        exceptionState.throwIfNeeded();
-        return;
-    }
-
     // None of these need to be RefPtr because info and context are guaranteed
     // to hold on to them.
     DOMWindow* window = V8Window::toImpl(info.Holder());
     LocalDOMWindow* source = callingDOMWindow(info.GetIsolate());
 
     ASSERT(window);
     UseCounter::countIfNotPrivateScript(info.GetIsolate(), window->frame(), UseCounter::WindowPostMessage);
 
+    ExceptionState exceptionState(ExceptionState::ExecutionContext, "postMessage", "Window", info.Holder(), info.GetIsolate());
+
     // If called directly by WebCore we don't have a calling context.
     if (!source) {
         exceptionState.throwTypeError("No active calling context exists.");
         exceptionState.throwIfNeeded();
         return;
     }
 
     // This function has variable arguments and can be:
     // Per current spec:
     //   postMessage(message, targetOrigin)
@@ skipping 173 matching lines @@
     v8::Handle<v8::Context> context = toV8Context(frame, DOMWrapperWorld::current(isolate));
     if (context.IsEmpty())
         return v8Undefined();
 
     v8::Handle<v8::Object> global = context->Global();
     ASSERT(!global.IsEmpty());
     return global;
 }
 
 } // namespace blink