Make <meter> transparent if -webkit-appearance:none or background CSS property is specified.

third_party/WebKit/Source/core/html/shadow/MeterShadowElement.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 20 matching lines @@
 #ifndef MeterShadowElement_h
 #define MeterShadowElement_h
 
 #include "core/html/HTMLDivElement.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 
 class HTMLMeterElement;
 
+class MeterFallbackElement : public HTMLDivElement {
+public:
+    DECLARE_NODE_FACTORY(MeterFallbackElement);
+
+private:
+    explicit MeterFallbackElement(Document&);
+    PassRefPtr<ComputedStyle> customStyleForLayoutObject() override;
+};
+
 class MeterShadowElement : public HTMLDivElement {
 protected:
     explicit MeterShadowElement(Document&);
     HTMLMeterElement* meterElement() const;
 
 private:
     bool layoutObjectIsNeeded(const ComputedStyle&) override;
 };
 
 class MeterInnerElement final : public MeterShadowElement {
 public:
     static PassRefPtrWillBeRawPtr<MeterInnerElement> create(Document&);
 
 private:
     explicit MeterInnerElement(Document&);
     bool layoutObjectIsNeeded(const ComputedStyle&) override;
     LayoutObject* createLayoutObject(const ComputedStyle&) override;
+    PassRefPtr<ComputedStyle> customStyleForLayoutObject() override;
 };
 
 class MeterBarElement final : public MeterShadowElement {
 private:
     explicit MeterBarElement(Document&);
 
 public:
     static PassRefPtrWillBeRawPtr<MeterBarElement> create(Document&);
 };
 
 class MeterValueElement final : public MeterShadowElement {
 public:
     static PassRefPtrWillBeRawPtr<MeterValueElement> create(Document&);
     void setWidthPercentage(double);
     void updatePseudo() { setShadowPseudoId(valuePseudoId()); }
 
 private:
     explicit MeterValueElement(Document&);
     const AtomicString& valuePseudoId() const;
 };
 
 }
 
 #endif // MeterShadowElement_h