[ES6 modules] Return previous error when an instantiation is reattempt.

third_party/WebKit/Source/core/testing/DummyModulator.cpp

Index: third_party/WebKit/Source/core/testing/DummyModulator.cpp
diff --git a/third_party/WebKit/Source/core/testing/DummyModulator.cpp b/third_party/WebKit/Source/core/testing/DummyModulator.cpp
index 3978fc079990615fbeb5b8ace61665d766dafff6..19a871791ff1b625d79e160541a7d79eb6033861 100644
--- a/third_party/WebKit/Source/core/testing/DummyModulator.cpp
+++ b/third_party/WebKit/Source/core/testing/DummyModulator.cpp
@@ -77,6 +77,11 @@ ScriptValue DummyModulator::InstantiateModule(ScriptModule) {
   return ScriptValue();
 }
 
+ScriptValue DummyModulator::GetInstantiationError(const ModuleScript*) {
+  NOTREACHED();
+  return ScriptValue();
+}
+
 Vector<String> DummyModulator::ModuleRequestsFromScriptModule(ScriptModule) {
   NOTREACHED();
   return Vector<String>();