toImplArguments should return HeapVector for Union types.

Source/bindings/core/v8/V8Binding.h

 /*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 * Copyright (C) 2012 Ericsson AB. 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.
@@ skipping 786 matching lines @@
     typedef NativeValueTraits<ValueType> TraitsType;
     result.reserveInitialCapacity(value.size());
     for (unsigned i = 0; i < value.size(); ++i) {
         result.uncheckedAppend(TraitsType::nativeValue(isolate, value[i].v8Value(), exceptionState));
         if (exceptionState.hadException())
             return VectorType();
     }
     return result;
 }
 
-template <typename T>
-Vector<T> toImplArguments(const v8::FunctionCallbackInfo<v8::Value>& info, int startIndex, ExceptionState& exceptionState)
+template <typename VectorType>
+VectorType toImplArguments(const v8::FunctionCallbackInfo<v8::Value>& info, int startIndex, ExceptionState& exceptionState)
 {
-    Vector<T> result;
-    typedef NativeValueTraits<T> TraitsType;
+    VectorType result;
+    typedef typename VectorType::ValueType ValueType;
+    typedef NativeValueTraits<ValueType> TraitsType;
     int length = info.Length();
     if (startIndex < length) {
         result.reserveInitialCapacity(length - startIndex);
         for (int i = startIndex; i < length; ++i) {
             result.uncheckedAppend(TraitsType::nativeValue(info.GetIsolate(), info[i], exceptionState));
             if (exceptionState.hadException())
-                return Vector<T>();
+                return VectorType();
         }
     }
     return result;
 }
 
 // Validates that the passed object is a sequence type per WebIDL spec
 // http://www.w3.org/TR/2012/CR-WebIDL-20120419/#es-sequence
 inline bool toV8Sequence(v8::Local<v8::Value> value, uint32_t& length, v8::Isolate* isolate, ExceptionState& exceptionState)
 {
     // Attempt converting to a sequence if the value is not already an array but is
@@ skipping 235 matching lines @@
 PassRefPtr<TraceEvent::ConvertableToTraceFormat> devToolsTraceEventData(v8::Isolate*, ExecutionContext*, v8::Local<v8::Function>);
 
 // Callback functions used by generated code.
 CORE_EXPORT void v8ConstructorAttributeGetter(v8::Local<v8::Name> propertyName, const v8::PropertyCallbackInfo<v8::Value>&);
 
 typedef void (*InstallTemplateFunction)(v8::Local<v8::FunctionTemplate>, v8::Isolate*);
 
 } // namespace blink
 
 #endif // V8Binding_h