Collect active stylesheets and and apply asynchronously.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 12 matching lines @@
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "core/frame/FrameView.h"
 
 #include "core/HTMLNames.h"
 #include "core/MediaTypeNames.h"
 #include "core/animation/DocumentAnimations.h"
 #include "core/css/FontFaceSet.h"
-#include "core/css/resolver/StyleResolver.h"
 #include "core/dom/AXObjectCache.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/dom/ElementVisibilityObserver.h"
 #include "core/dom/Fullscreen.h"
 #include "core/dom/IntersectionObserverCallback.h"
 #include "core/dom/IntersectionObserverController.h"
 #include "core/dom/IntersectionObserverInit.h"
+#include "core/dom/StyleChangeReason.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/RenderedPosition.h"
 #include "core/editing/markers/DocumentMarkerController.h"
 #include "core/events/ErrorEvent.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/frame/BrowserControls.h"
 #include "core/frame/EventHandlerRegistry.h"
 #include "core/frame/FrameHost.h"
@@ skipping 1405 matching lines @@
 void FrameView::adjustMediaTypeForPrinting(bool printing) {
   if (printing) {
     if (m_mediaTypeWhenNotPrinting.isNull())
       m_mediaTypeWhenNotPrinting = mediaType();
     setMediaType(MediaTypeNames::print);
   } else {
     if (!m_mediaTypeWhenNotPrinting.isNull())
       setMediaType(m_mediaTypeWhenNotPrinting);
     m_mediaTypeWhenNotPrinting = nullAtom;
   }
+
+  m_frame->document()->setNeedsStyleRecalc(

[esprehn, 2016/12/09 01:36:21]

Ouch, did this code path always force a full document recalc?

[rune, 2016/12/09 08:55:50]

Yes, that is, setMediaType() called from here calls
mediaQueryAffectingValueChanged() which used to cause a full document recalc
regardlessly through resolverChanged(FullStyleUpdate).
mediaQueryAffectingValueChanged() now only has an effect if media queries
actually did change evaluation. If I leave this out, I'll have regressions in
tests for printing and zoom, at least. That is because of [1]. There might be
other switches on document().printing() which currently also requires
recalc/relayout if zoom factor is different from 1. We can surely improve on
this, but I think that could be a separate task.

Perhaps the setNeedsStyleRecalc() call here should be moved to setMediaType? I
looks like we only call setMediaType for switching between print and the other
media type (always screen?).

[1]
https://codesearch.chromium.org/chromium/src/third_party/WebKit/Source/core/c...

+      SubtreeStyleChange,
+      StyleChangeReasonForTracing::create(StyleChangeReason::StyleSheetChange));
 }
 
 bool FrameView::contentsInCompositedLayer() const {
   LayoutViewItem layoutViewItem = this->layoutViewItem();
   return !layoutViewItem.isNull() &&
          layoutViewItem.compositingState() == PaintsIntoOwnBacking;
 }
 
 void FrameView::addBackgroundAttachmentFixedObject(LayoutObject* object) {
   ASSERT(!m_backgroundAttachmentFixedObjects.contains(object));
@@ skipping 3183 matching lines @@
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.width();
 }
 
 int FrameView::initialViewportHeight() const {
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.height();
 }
 
 }  // namespace blink