Add a UA style, "display: contents", for <slot>

third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 19 matching lines @@
 
 #include "core/css/CSSDefaultStyleSheets.h"
 
 #include "core/MathMLNames.h"
 #include "core/css/MediaQueryEvaluator.h"
 #include "core/css/RuleSet.h"
 #include "core/css/StyleSheetContents.h"
 #include "core/dom/Fullscreen.h"
 #include "core/html/HTMLAnchorElement.h"
 #include "core/html/HTMLHtmlElement.h"
+#include "core/html/HTMLSlotElement.h"
 #include "core/layout/LayoutTheme.h"
 #include "platform/PlatformResourceLoader.h"
 #include "wtf/LeakAnnotations.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 CSSDefaultStyleSheets& CSSDefaultStyleSheets::instance() {
   DEFINE_STATIC_LOCAL(CSSDefaultStyleSheets, cssDefaultStyleSheets,
@@ skipping 102 matching lines @@
       (isHTMLVideoElement(element) || isHTMLAudioElement(element))) {
     String mediaRules = loadResourceAsASCIIString("mediaControls.css") +
                         LayoutTheme::theme().extraMediaControlsStyleSheet();
     m_mediaControlsStyleSheet = parseUASheet(mediaRules);
     m_defaultStyle->addRulesFromSheet(mediaControlsStyleSheet(), screenEval());
     m_defaultPrintStyle->addRulesFromSheet(mediaControlsStyleSheet(),
                                            printEval());
     changedDefaultStyle = true;
   }
 
+  if (isHTMLSlotElement(element) &&
+      RuntimeEnabledFeatures::cssDisplayContentsEnabled() &&
+      !m_slotStyleSheet) {

[kochi, 2016/11/01 06:43:13]

If the reason for having a separate UA stylesheet file only for
<slot> element is to gate the behavior by the runtime flag, could
you add a TODO for merging slot.css into html.css once
CSSDisplayContents flag gets enabled?

[rune, 2016/11/01 07:38:17]

I think we might as well add it to html.css. When display:contents is not
supported, we will end up with an empty rule for slot, which is OK I think.
Alternatively, you can conditionally add the slot.css source to the defaultRules
string in the constructor. Having it here, means we'll get a re-collection of
document rule features when we see a slot element the first time. I think it's
better to parse the slot rule unconditionally.

+    m_slotStyleSheet = parseUASheet(loadResourceAsASCIIString("slot.css"));
+    m_defaultStyle->addRulesFromSheet(slotStyleSheet(), screenEval());
+    m_defaultPrintStyle->addRulesFromSheet(slotStyleSheet(), printEval());
+    changedDefaultStyle = true;
+  }
+
   ASSERT(!m_defaultStyle->features().hasIdsInSelectors());
   ASSERT(m_defaultStyle->features().siblingRules.isEmpty());
   return changedDefaultStyle;
 }
 
 void CSSDefaultStyleSheets::ensureDefaultStyleSheetForFullscreen() {
   if (m_fullscreenStyleSheet)
     return;
 
   String fullscreenRules = loadResourceAsASCIIString("fullscreen.css") +
@@ skipping 10 matching lines @@
   visitor->trace(m_defaultViewSourceStyle);
   visitor->trace(m_defaultStyleSheet);
   visitor->trace(m_mobileViewportStyleSheet);
   visitor->trace(m_televisionViewportStyleSheet);
   visitor->trace(m_xhtmlMobileProfileStyleSheet);
   visitor->trace(m_quirksStyleSheet);
   visitor->trace(m_svgStyleSheet);
   visitor->trace(m_mathmlStyleSheet);
   visitor->trace(m_mediaControlsStyleSheet);
   visitor->trace(m_fullscreenStyleSheet);
+  visitor->trace(m_slotStyleSheet);
 }
 
 }  // namespace blink