Run Microtasks before dispatching onload

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index cf01ec8247ede9efbf6276774aef53b647140f67..f03d84601cd1ed5b0cf9d082c6dbfff01ef67205 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -77,6 +77,7 @@
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContextTask.h"
 #include "core/dom/MainThreadTaskRunner.h"
+#include "core/dom/Microtask.h"
 #include "core/dom/MutationObserver.h"
 #include "core/dom/NodeChildRemovalTracker.h"
 #include "core/dom/NodeFilter.h"
@@ -4627,6 +4628,9 @@ void Document::finishedParsing()
         m_documentTiming.domContentLoadedEventEnd = monotonicallyIncreasingTime();
     setParsingState(FinishedParsing);
 
+    // Empty microtask queue to ensure custom element is resolved before onload event.

[dominicc (has gone to gerrit), 2014/12/17 14:31:03]

I would remove this and put a FIXME with a link to the HTML spec that says to
spin the event loop before dispatching DOMContentLoaded and note that this is
simulating that.

[kouhei (in TOK), 2014/12/18 05:33:55]

Done.

+    Microtask::performCheckpoint();
+
     // The loader's finishedParsing() method may invoke script that causes this object to
     // be dereferenced (when this document is in an iframe and the onload causes the iframe's src to change).
     // Keep it alive until we are done.