Throw exception for null listener in addEventListener

sky/engine/tonic/dart_exception_factory.cc

Index: sky/engine/tonic/dart_exception_factory.cc
diff --git a/sky/engine/tonic/dart_exception_factory.cc b/sky/engine/tonic/dart_exception_factory.cc
index 52b57092792c306ad638e3a4b12268390a722e4f..98f9675390bdb70121d8003ef85bec435a22d324 100644
--- a/sky/engine/tonic/dart_exception_factory.cc
+++ b/sky/engine/tonic/dart_exception_factory.cc
@@ -7,6 +7,7 @@
 
 #include "sky/engine/tonic/dart_converter.h"
 #include "sky/engine/tonic/dart_builtin.h"
+#include "sky/engine/wtf/text/StringBuilder.h"
 
 namespace blink {
 
@@ -17,6 +18,14 @@ DartExceptionFactory::DartExceptionFactory(DartState* dart_state)
 DartExceptionFactory::~DartExceptionFactory() {
 }
 
+Dart_Handle DartExceptionFactory::CreateNullArgumentException(int index) {
+  StringBuilder message;
+  message.appendLiteral("Argument ");
+  message.appendNumber(index);
+  message.appendLiteral(" cannot be null.");
+  return CreateException("ArgumentError", message.toString());
+}
+
 Dart_Handle DartExceptionFactory::CreateException(const String& class_name,
                                                   const String& message) {
   if (core_library_.is_empty()) {