IDL: Support optional argument default value syntax

Source/bindings/v8/V8Binding.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 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 476 matching lines @@
 }
 
 float toFloat(v8::Handle<v8::Value> value, ExceptionState& exceptionState)
 {
     TONATIVE_DEFAULT_EXCEPTIONSTATE(v8::Local<v8::Number>, numberObject, value->ToNumber(), exceptionState, 0);
     return numberObject->NumberValue();
 }
 
 String toByteString(v8::Handle<v8::Value> value, ExceptionState& exceptionState)
 {
-    // Handle [Default=NullString]
+    // Handle null default value.
     if (value.IsEmpty())
         return String();
 
     // From the Web IDL spec: http://heycam.github.io/webidl/#es-ByteString
 
     // 1. Let x be ToString(v)
     TONATIVE_DEFAULT_EXCEPTIONSTATE(v8::Local<v8::String>, stringObject, value->ToString(), exceptionState, String());
     String x = toCoreString(stringObject);
 
     // 2. If the value of any element of x is greater than 255, then throw a TypeError.
@@ skipping 302 matching lines @@
 PassRefPtr<TraceEvent::ConvertableToTraceFormat> devToolsTraceEventData(ExecutionContext* context, v8::Handle<v8::Function> function, v8::Isolate* isolate)
 {
     int scriptId = 0;
     String resourceName;
     int lineNumber = 1;
     GetDevToolsFunctionInfo(function, isolate, scriptId, resourceName, lineNumber);
     return InspectorFunctionCallEvent::data(context, scriptId, resourceName, lineNumber);
 }
 
 } // namespace WebCore