Introduce :-internal-shadow-host-has-appearance pseudo class, and apply it to METER element.

third_party/WebKit/Source/core/css/SelectorChecker.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, 2013 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/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 899 matching lines @@
         return context.scope == &element;
     case CSSSelector::PseudoUnresolved:
         return element.isUnresolvedCustomElement();
     case CSSSelector::PseudoHost:
     case CSSSelector::PseudoHostContext:
         return checkPseudoHost(context, result);
     case CSSSelector::PseudoSpatialNavigationFocus:
         return m_isUARule && matchesSpatialNavigationFocusPseudoClass(element);
     case CSSSelector::PseudoListBox:
         return m_isUARule && matchesListBoxPseudoClass(element);
+    case CSSSelector::PseudoHostHasAppearance:
+        if (!m_isUARule)

[esprehn, 2016/05/09 19:39:50]

this should check that containingShadowRoot()->type() is a UserAgentShadowRoot.

[tkent, 2016/05/10 04:29:29]

Done.

+            return false;
+        if (!element.shadowHost())
+            return false;
+        if (!element.shadowHost()->computedStyle())

[esprehn, 2016/05/09 19:39:50]

Don't call computedStyle repeatedly, save to a local and null check that.

[tkent, 2016/05/10 04:29:29]

Done.

+            return false;
+        return element.shadowHost()->computedStyle()->hasAppearance();
     case CSSSelector::PseudoWindowInactive:
         if (!context.hasSelectionPseudo)
             return false;
         return !element.document().page()->focusController().isActive();
     case CSSSelector::PseudoHorizontal:
     case CSSSelector::PseudoVertical:
     case CSSSelector::PseudoDecrement:
     case CSSSelector::PseudoIncrement:
     case CSSSelector::PseudoStart:
     case CSSSelector::PseudoEnd:
@@ skipping 23 matching lines @@
             subContext.scope = nullptr;
             subContext.treatShadowHostAsNormalScope = false;
 
             for (subContext.selector = selector.selectorList()->first(); subContext.selector; subContext.selector = CSSSelectorList::next(*subContext.selector)) {
                 if (match(subContext))
                     return true;
             }
             return false;
         }
     case CSSSelector::PseudoWebKitCustomElement:
-        {
-            if (ShadowRoot* root = element.containingShadowRoot())
-                return root->type() == ShadowRootType::UserAgent && element.shadowPseudoId() == selector.value();
-            return false;
+        if (ShadowRoot* root = element.containingShadowRoot()) {
+            if (selector.value().startsWith("-webkit-internal-") && !m_isUARule)

[esprehn, 2016/05/09 19:39:50]

why do we need this? We should just make the pseudo only apply inside a UA
shadow.

[tkent, 2016/05/10 04:29:29]

We should avoid to expose new vendor-specific pseudo elements.

+                return false;
+            return root->type() == ShadowRootType::UserAgent && element.shadowPseudoId() == selector.value();
         }
+        return false;
     case CSSSelector::PseudoSlotted:
         {
             SelectorCheckingContext subContext(context);
             subContext.isSubSelector = true;
             subContext.scope = nullptr;
             subContext.treatShadowHostAsNormalScope = false;
 
             // ::slotted() only allows one compound selector.
             ASSERT(selector.selectorList()->first());
             ASSERT(!CSSSelectorList::next(*selector.selectorList()->first()));
@@ skipping 157 matching lines @@
 }
 
 bool SelectorChecker::matchesFocusPseudoClass(const Element& element)
 {
     if (InspectorInstrumentation::forcePseudoState(const_cast<Element*>(&element), CSSSelector::PseudoFocus))
         return true;
     return element.focused() && isFrameFocused(element);
 }
 
 } // namespace blink