IDL dictionary: Throw a TypeError when an interface member conversion fails

Source/bindings/templates/dictionary_v8.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file has been auto-generated by {{code_generator}}. DO NOT MODIFY!
 
 #include "config.h"
 #include "{{v8_original_class}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % v8_class %}
@@ skipping 34 matching lines @@
         // Do nothing.
     {% if member.is_nullable %}
     } else if ({{member.name}}Value->IsNull()) {
         impl.{{member.null_setter_name}}();
     {% endif %}
     } else {
         {% if member.use_output_parameter_for_result %}
         {{member.cpp_type}} {{member.name}};
         {% endif %}
         {{member.v8_value_to_local_cpp_value}};
+        {% if member.is_interface_type %}
+        if (!{{member.name}} && !{{member.name}}Value->IsNull()) {
+            exceptionState.throwTypeError("member {{member.name}} is not of type {{member.idl_type}}.");
+            return;
+        }
+        {% endif %}
         {% if member.enum_validation_expression %}
         String string = {{member.name}};
         if (!({{member.enum_validation_expression}})) {
             exceptionState.throwTypeError("member {{member.name}} ('" + string + "') is not a valid enum value.");
             return;
         }
         {% elif member.is_object %}
         if (!{{member.name}}.isObject()) {
             exceptionState.throwTypeError("member {{member.name}} is not an object.");
             return;
@@ skipping 33 matching lines @@
 }
 
 {{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(const v8::Handle<v8::Value>& value, v8::Isolate* isolate, ExceptionState& exceptionState)
 {
     {{cpp_class}} impl;
     {{v8_class}}::toImpl(isolate, value, impl, exceptionState);
     return impl;
 }
 
 } // namespace blink