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

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

Index: Source/bindings/core/v8/custom/V8WindowCustom.cpp
diff --git a/Source/bindings/core/v8/custom/V8WindowCustom.cpp b/Source/bindings/core/v8/custom/V8WindowCustom.cpp
index cd38053741c40b59e361d5264c23dcdc410cc6e8..4a8d935ab28e4d63cfd619b54e033b0cebc8c6b1 100644
--- a/Source/bindings/core/v8/custom/V8WindowCustom.cpp
+++ b/Source/bindings/core/v8/custom/V8WindowCustom.cpp
@@ -159,13 +159,6 @@
 
 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());
@@ -173,6 +166,8 @@
 
     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) {