[ES6 modules] ModulatorImpl::ExecuteModule should report error acquir…

…ed via GetError

Before this CL, ExecuteModule reported error acquired via
ModuleScript::GetErrorInternal. This is not always correct after
40485cc. ModuleScript::GetErrorInternal only
refers to preinstantiation errors, and we may have errors stored inside
module records as [[ErrorCompletion]] field's [[Value]].

This CL corrects ExecuteModule to report the appropriate error by using error
acquired by ModulatorImpl::GetError, which correctly implements the
"#concept-module-script-error" spec concept.

This is tested by wpt/html/semantics/scripting-1/the-script-element/module/evaluation-error-*.html.
However the wpt tests don't pass until we have updated

Bug: 594639, 727299, whatwg/html#2674 , tc39/ecma262#916
Change-Id: I97de9762bfad58e1f1b71bedf524761e53d43158
Reviewed-on: https://chromium-review.googlesource.com/558725
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483908}

third_party/WebKit/Source/core/dom/ModulatorImpl.cpp

@@ -214,10 +214,10 @@ void ModulatorImpl::ExecuteModule(const ModuleScript* module_script) {
   // Step 3. "If s is errored, then report the exception given by s's error for
   // s and abort these steps." [spec text]
   if (module_script->IsErrored()) {
-    v8::Isolate* isolate = script_state_->GetIsolate();
-    ScriptModule::ReportException(
-        script_state_.Get(), module_script->CreateErrorInternal(isolate),
-        module_script->BaseURL().GetString(), module_script->StartPosition());
+    ScriptValue error = GetError(module_script);
+    ScriptModule::ReportException(script_state_.Get(), error.V8Value(),
+                                  module_script->BaseURL().GetString(),
+                                  module_script->StartPosition());
     return;
   }