bindings: Throw exceptions when required dictionary members aren't passed

third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp

 {% from 'utilities.cpp' import declare_enum_validation_variable %}
 {% include 'copyright_block.txt' %}
 #include "{{v8_original_class}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % v8_class %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace blink {
 
 {% from 'utilities.cpp' import v8_value_to_local_cpp_value %}
 void {{v8_class}}::toImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8Value, {{cpp_class}}& impl, ExceptionState& exceptionState)
 {
-    if (isUndefinedOrNull(v8Value))
+    if (isUndefinedOrNull(v8Value)) {
+        {% if required_member_names %}
+        exceptionState.throwTypeError("Missing required member(s): {{required_member_names|join(', ')}}.");
+        {% endif %}
         return;
+    }
     if (!v8Value->IsObject()) {
         {% if use_permissive_dictionary_conversion %}
         // Do nothing.
         return;
         {% else %}
         exceptionState.throwTypeError("cannot convert to dictionary.");
         return;
         {% endif %}
     }
 
@@ skipping 98 matching lines @@
 }
 
 {{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(v8::Isolate* isolate, v8::Local<v8::Value> value, ExceptionState& exceptionState)
 {
     {{cpp_class}} impl;
     {{v8_class}}::toImpl(isolate, value, impl, exceptionState);
     return impl;
 }
 
 } // namespace blink