Run Microtasks before dispatching onload

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 59 matching lines @@
 #include "core/dom/DocumentLifecycleObserver.h"
 #include "core/dom/DocumentMarkerController.h"
 #include "core/dom/DocumentType.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementDataCache.h"
 #include "core/dom/ElementRegistrationOptions.h"
 #include "core/dom/ElementTraversal.h"
 #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"
 #include "core/dom/NodeIterator.h"
 #include "core/dom/NodeRareData.h"
 #include "core/dom/NodeRenderStyle.h"
 #include "core/dom/NodeRenderingTraversal.h"
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/NodeWithIndex.h"
 #include "core/dom/ProcessingInstruction.h"
@@ skipping 4519 matching lines @@
 PassRefPtrWillBeRawPtr<DocumentNameCollection> Document::documentNamedItems(const AtomicString& name)
 {
     return ensureCachedCollection<DocumentNameCollection>(DocumentNamedItems, name);
 }
 
 void Document::finishedParsing()
 {
     ASSERT(!scriptableDocumentParser() || !m_parser->isParsing());
     ASSERT(!scriptableDocumentParser() || m_readyState != Loading);
     setParsingState(InDOMContentLoaded);
+
+    // FIXME: DOMContentLoaded should be dispatched in a queued task,

[dominicc (has gone to gerrit), 2015/01/05 07:29:39]

I think a good FIXME does three things:

1. Keeps it short.
2. Explains what needs to be fixed.
3. Explains when the FIXME can be addressed.

I think you don't need the comment here, because it's not a FIXME as much as an
actual bug, so you could comment on Issue 425790 directly. The spec links are
probably useful in the bug thread?

Below I think you want something like:

// Ensure Custom Element callbacks are drained before DOMContentLoaded.
// FIXME: Remove this ad-hoc checkpoint when DOMContentLoaded is dispatched in a
queued task, which will do a checkpoint anyway. (Issue 425790)

[kouhei (in TOK), 2015/01/06 01:37:05]

Done.

+    // but we are dispatching this synchronously at the moment.
+    // Spec: Section 12.2.6 "The end" step 4 and 5:
+    // https://html.spec.whatwg.org/multipage/syntax.html#the-end
+    // See https://crbug.com/425790
     if (!m_documentTiming.domContentLoadedEventStart)
         m_documentTiming.domContentLoadedEventStart = monotonicallyIncreasingTime();
     dispatchEvent(Event::createBubble(EventTypeNames::DOMContentLoaded));
     if (!m_documentTiming.domContentLoadedEventEnd)
         m_documentTiming.domContentLoadedEventEnd = monotonicallyIncreasingTime();
     setParsingState(FinishedParsing);
+    // Perform microtask checkpoint here as a partial fix to make this closer to spec.
+    // FIXME: This should be removed once the above dispatchEvent(DOMContentLoaded) is done asynchronously.
+    // Spec: Section 12.2.6 "Spin the event loop" step 5 says we should spin the event loop here:
+    // https://html.spec.whatwg.org/multipage/syntax.html#the-end
+    // Spinning the event loop includes performing a microtask checkpoint:
+    // https://html.spec.whatwg.org/multipage/webappapis.html#spin-the-event-loop
+    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.
     RefPtrWillBeRawPtr<Document> protect(this);

[dominicc (has gone to gerrit), 2015/01/05 07:29:39]

Why doesn't this protect need to be moved to before
Microtask::performCheckpoint? Can't the checkpoint also invoke script?

[kouhei (in TOK), 2015/01/06 01:37:05]

Done.

 
     if (RefPtrWillBeRawPtr<LocalFrame> frame = this->frame()) {
         // Don't update the render tree if we haven't requested the main resource yet to avoid
         // adding extra latency. Note that the first render tree update can be expensive since it
         // triggers the parsing of the default stylesheets which are compiled-in.
         const bool mainResourceWasAlreadyRequested = frame->loader().stateMachine()->committedFirstRealDocumentLoad();
 
         // FrameLoader::finishedParsing() might end up calling Document::implicitClose() if all
         // resource loads are complete. HTMLObjectElements can start loading their resources from
         // post attach callbacks triggered by recalcStyle().  This means if we parse out an <object>
@@ skipping 1201 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif