Generate a bit less code to handle failed arity checks.

Source/bindings/v8/ExceptionState.cpp

Index: Source/bindings/v8/ExceptionState.cpp
diff --git a/Source/bindings/v8/ExceptionState.cpp b/Source/bindings/v8/ExceptionState.cpp
index 77c9103d7be7afe21926f028d6d315689b8af907..a557db9599c3255e8024fef5e00b070cb2392d4b 100644
--- a/Source/bindings/v8/ExceptionState.cpp
+++ b/Source/bindings/v8/ExceptionState.cpp
@@ -83,6 +83,12 @@ void ExceptionState::throwTypeError(const String& message)
     setException(V8ThrowException::createTypeError(addExceptionContext(message), m_isolate));
 }
 
+void ExceptionState::notEnoughArguments(int expected, int actual)
+{
+    throwTypeError(ExceptionMessages::notEnoughArguments(expected, actual));
+    throwIfNeeded();

[Mike West, 2013/12/05 11:48:59]

This is a change from the semantics we've set up for ExceptionState. Generally,
we pass the state somewhere, allow that somewhere to queue up an exception, and
then _actually_ throw the exception when we get back to bindings.

I'd prefer to keep that implicit contract, even if it means that throwing
exceptions _from_ bindings is a bit more verbose.

[sof, 2013/12/05 12:01:32]

It seems redundant to generate that much code at each site doing an arity check.

Contract expectations can be accounted for by naming, I think. I didn't prefix
"throw" as it isn't throwing a non-existent NotEnoughArguments exception.
Perhaps "report" or some such would be clearer.

[Mike West, 2013/12/05 12:15:15]

As long as we can assume that this is always called in the same context in which
the ExceptionState was created, I agree with you. If I pass 'exceptionState'
into a function, however, I don't want a situation where 'throwIfNeeded' might
be called both by the callee and the caller.
 
Sure. This comes back to one of the other questions. When do we want the
callsite to call 'throwDOMException' or 'throwTypeException' with an appropriate
message, and when do we want to wrap those to set the message implicitly?

+}
+
 void TrackExceptionState::throwDOMException(const ExceptionCode& ec, const String& message)
 {
     m_code = ec;