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

third_party/WebKit/Source/core/dom/Element.h

Index: third_party/WebKit/Source/core/dom/Element.h
diff --git a/third_party/WebKit/Source/core/dom/Element.h b/third_party/WebKit/Source/core/dom/Element.h
index cb15e383d557763553b27bf7dcadec94ce5c7aa8..ca254c77f078a2fa6a7f69dd74ebf38992920f07 100644
--- a/third_party/WebKit/Source/core/dom/Element.h
+++ b/third_party/WebKit/Source/core/dom/Element.h
@@ -450,6 +450,9 @@ public:
     virtual String defaultToolTip() const { return String(); }
 
     virtual const AtomicString& shadowPseudoId() const;
+    // The specified string must start with "-webkit-" or "-internal-". The
+    // former can be used as a selector in any places, and the latter can be
+    // used only in UA stylesheet.
     void setShadowPseudoId(const AtomicString&);
 
     LayoutSize minimumSizeForResizing() const;